Using an additive to fix a rear main seal leak
- Thread starter DaveK22
- Start date
Another vote for Napa hi mileage 10w-30.
A few months back I developed a pretty annoying rms leak. I had been using Castrol 5w-30, because I refused to believe my neighbor who is a jeep guru, who advised me to always use conventional oil. I’ve always been a “Castrol guy”.
Anyways a combination of not driving the jeep, switching to Castrol 10w-30 conventional, but then back to 5w-30 because of a brief lifter noise on startup. Then it started leaking.
Tried the Napa high mileage after reading this thread a few weeks ago.
Leak stopped after a week or so.
Probably too early to be bragging about it, but I’m really pleased to have avoided the rms replacement so far.
I say give it a try before you try anything more extreme. And give it a couple weeks to condition the seal or whatever the heck it does. The oil was on sale too!
I consider Bransford to be one of the gurus on this forum, so I took his advice. Thank you, Sir!
A few months back I developed a pretty annoying rms leak. I had been using Castrol 5w-30, because I refused to believe my neighbor who is a jeep guru, who advised me to always use conventional oil. I’ve always been a “Castrol guy”.
Anyways a combination of not driving the jeep, switching to Castrol 10w-30 conventional, but then back to 5w-30 because of a brief lifter noise on startup. Then it started leaking.
Tried the Napa high mileage after reading this thread a few weeks ago.
Leak stopped after a week or so.
Probably too early to be bragging about it, but I’m really pleased to have avoided the rms replacement so far.
I say give it a try before you try anything more extreme. And give it a couple weeks to condition the seal or whatever the heck it does. The oil was on sale too!
I consider Bransford to be one of the gurus on this forum, so I took his advice. Thank you, Sir!
In my opinion, from a 35 year Toyota Master Diagnostic Technician is to replace the seal with the factory seal and follow the repair manual procedure and the leak will be fixed. Worked on my 06 LJ.
Mine leaks. I put a piece of cardboard under the Jeep so it doesn't drip on the garage floor. It didn’t leak enough in two years to notice it on the dipstick. Sometimes the spot looks bigger then it's really leaking.
I finally changed the oil even though I only had 6,000 miles on the oil after 2 years of Covid driving.
Does it drip or drain? I'd check the oil more regularly unless it's big.
I finally changed the oil even though I only had 6,000 miles on the oil after 2 years of Covid driving.
Does it drip or drain? I'd check the oil more regularly unless it's big.
I had a very slow 2-drops-a-month leak when I bought my Wrangler.
After a few months, I topped up the oil with what I had on hand, some 5W-30 from a previous vehicle (probably a syn-blend), because I didn't want to run to the store for a single quart. I only added a few ounces, and it started leaking within a few days, several drops a day. I let it drip like that for several weeks, and it was quite consistent.
I changed the oil to 10W-30 conventional, and within 2 days the leak completely stopped. Not a drop in the last three weeks.
I'm amazed that even a few ounces of low-viscosity synthetic could make that much difference.
After a few months, I topped up the oil with what I had on hand, some 5W-30 from a previous vehicle (probably a syn-blend), because I didn't want to run to the store for a single quart. I only added a few ounces, and it started leaking within a few days, several drops a day. I let it drip like that for several weeks, and it was quite consistent.
I changed the oil to 10W-30 conventional, and within 2 days the leak completely stopped. Not a drop in the last three weeks.
I'm amazed that even a few ounces of low-viscosity synthetic could make that much difference.
Great example of having the spend more dealer mentality. You'd replace the RMS and charge the customer $800-1600 or whatever a Toyota RMS replacement costs rather than just restore the seal back to a non-leaking consistency with a simple inexpensive change to a different motor oil? No wonder I always hated going to the dealer.
My daily driver BMW started leaking badly from its RMS years ago and the local BMW shops wanted $1600-1700 to replace it. I checked some BMW forums who all said to just change from a synthetic to a high mileage conventional so I did so and the RMS stopped leaking within a week.
Jerry - would you still recommend the high mileage option for a lower mileage Jeep (under 55,000) or use a conventional 10W - 30? No leaks currently.
It wouldn't hurt. NAPA (made by Valvoline) High Mileage conventional 10W-30 is a good choice.
Not expensive... I do it myself but I get your point. I just prefer fix the problem and not bandaid it.
Restoring a dried out seal to its original consistency with the seal restoring additives contained in a high mileage engine oil is not a bandaid approach.
FYI, It’s July 2023 and my RMS is still not leaking.
I have 3 big jugs of the Napa oil squirreled away in my garage.
Thanks Jerry!
Larry Parrish
New Member
Before I saw Jerry's suggestion, I had the RMS leak and I tried several of the additives, Lucas, Bars, and the At-205. I had been using Valvoline Synthetic. None of them worked. It actually seemed to be getting worse. I was getting desperate, especially after reading the stories about replaced RMS and that not curing the problem. Then I saw Jerry's remedy and I saw another post that suggested a little heavier weight oil so I did both. I went back to conventional oil, Shell 15W-40. it was available on Amazon in gallon containers. After about 700 miles the leak has completely stopped, but I saw a reduction in the leak very quickly after only a few miles. Thanks Jerry for your suggestion. It's really appreciated.
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deadbeat son
TJ Addict
I'm also reaching out to thank @Jerry Bransford here - I recently purchased a 35k mile '05 TJ that is in VERY nice condition. When I got it home, I noticed it was marking its territory wherever I parked it. After looking more closely, I could see oil oozing out of the RMS area and down the flywheel inspection plate. I had a feeling that it was leaking due to seal contraction from a lack of regular use, so I changed the oil to Napa high mileage 10-30 (which is a synthetic blend) and drove the Jeep for 200 miles. When I got home, it didn't drip onto my garage floor. I cleaned up the inspection cover, and now 2 weeks later it still hasn't dripped a drop. I'm so happy not to have to change the RMS in this Jeep! Thanks Jerry.
It’s May 2025. A few months ago my RMS, starting leaking a bit. I hadn’t changed the oil in well over a year, hadn’t driven the jeep much either.
So I changed the oil and filter, using the NAPA stuff, of course.
And guess what? The leak went away again.
I need to buy another couple jugs to replenish my stash.
So I changed the oil and filter, using the NAPA stuff, of course.
And guess what? The leak went away again.
I need to buy another couple jugs to replenish my stash.
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