Product to stop oil leak?

Those kind of things might work, but I’ve always thought they could plug something up that it shouldn’t and cause more problems.

Are you seeing oil spots on the ground? Areas of the engine? If so, where?

Or are you seeing no visible leaks but losing oil on the dipstick?
 
So after failing to find where my mysterious oil leak is coming from, I've decided to add an oil additive to stop the oil leak. What is good and what is crap? I don't want to ruin my 4.0

The best plan to take care of your 4.o is to address the source of the leak and repair it. I'm sure there's enough experience on this forum to help you find it.
 
Most oil brands have their 'High Milage' oil added to help with degrading seals. Anything more aggressive like an 8 oz bottle of Supeer Ultra seal Sweller Deluxe can do more harm than good. Swelling the seals that don't leak to the point that they do. Rear main and valve cover seem to go first after such a product.
 
So after failing to find where my mysterious oil leak is coming from, I've decided to add an oil additive to stop the oil leak. What is good and what is crap? I don't want to ruin my 4.0

I highly advise against those types of additives unless you don't care about your engine. As much of a pain in the butt as it can be to find an oil leak, find it, don't band aid it. You'll just do more damage in the long run. With that said, if you are going to go ahead and add it, I would recommend Lucas products.

https://www.jegs.com/webapp/wcs/sto...&submodel=&engine=&Nrpp=&No=&persistYmm=false