A while back the rear main seal on my dads 99 XJ with a 4.0 just exploded..... it flew out dumped tons of oil yada yada. After replacing it, it was fine. The Jeep is now mine two years later and leaking.... again..... I pulled the pan and there it was.... part of the rear main..... why?

How is your blowby? Is pressure building up in the crankcase?

What he said ^^,

Plus, maybe it wasn't done quite right the first time, so you only got two years out of it. I'd look at that blowby issue, though, before assuming that.

I've come to the conclusion that all RMSs are not equal.

I purchased a "top quality" rebuild kit from a reputable source I have used in the past to major this 4.0.
By and large the components were recognizable US names, but the rear main seal was just in a plastic unmarked bag.

It lasted two months, and then like turning on a faucet, it leaked like a MFer.

I did nothing else than pull down the pan and replace it with a Fel Pro one.
No leaks, nothing since.

I haven’t checked it, it’s a really good motor with no knocks or anything like that.... and also my dad used a felpro gasket. It’s what I used too. If there’s a lot of blowby any suggestions to just let the pressure release so I don’t have this problem?