Well, I'm new to Jeeps, TJs, and the 4.0, and I haven't messed with that area on my LJ, yet, so take my advice with more than a grain of salt. On most vehicles I've messed with, that's just a dust cover, it's not sealed. The rear main seal on the engine and the front main seal on the transmission are what keeps "stuff" out of both. If it were mine, I'd loosen the two screws on either side of the bend just enough to allow the cover to "float" under the screws. I'd then take a long screwdriver, place it vertical, handle-side down, just behind that cover and in front of the oil pan, and leverage the cover as flat as I could get it. Then, tighten the screws and call it good. If, because Jeeps are known to be run through mudholes, the engineers put a seal there, disregard what I just wrote. Looking at the parts manual for my 2005 LJ, there is no seal there. Not sure about your 2000...