Hey forum, I've been giving my 92 XJ some much needed attention over the past few weeks starting by addressing oil and fluid leaks. Pertaining to oil, here is a list of what I've replaced:

Oil filler cap
Oil filter
Oil filter adapter rings
Valve cover gasket
Oil pan gasket (With gasket and RTV)
Rear main seal

My leak spots under the jeep have significantly improved (decreased) but I'm still seeing and smelling smoke come from under the jeep like when I come to a stop in traffic, and I'm still seeing spots underneath on concrete about the size of a quarter/half dollar after I let it run and then sit. Theres still oil on the cross member near the transfer case and some fresh oil is still making it's way down to the lowest point on the oil pan itself.
Only seems to leak after it runs a little bit.

Did I forget a gasket that typically goes bad?

 

Check for oil on the transfer case below the transfer case output seal. It gets slung up to the floor when running and will drip from the tailcone also.
It will also run down to the drain bolt and drip off from there which can be the from the case half to tailcone seal/speed sender gasket where the gear is/transfer case output seal or a combination.

The distributor gasket is sometimes known to leak too.

Eliminate the oil leaks.
If there is no oil on the bottom of the oil filter then the adapter gaskets are good
Back of the head for the valve cover

 

A bad oil pressure sending unit ( located right on top of the oil filter adapter) can leak also. Might wanna check that out also

 

Thoroughly clean the engine bay & underside.
Then look for leaks that will lead you to the source.

 

My most recent one was the oil pressure sensor adapter, madman has it clean it up and then inspect. I wish I had..........

 

I'd be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn't own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking.

Many mechanics, friends, people on Jeep forums who can’t see your Jeep from where they’re at, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don't jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons.

First off, the engine sits nose-up and any oil will run back to the RMS area. Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber's adage apply here. "$hit flows downhill".

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.

Revised 02-26-2013

 

If you have any kind of coolant leaks those can be confused with oil leaks too. For instance if you have a small coolant leak higher up on the engine, but your engine is covered in grease/old oil, but the time the coolant gets to the bottom it's all oily and looks like an oil leak. Sames thing with power steering fluid leaks from the pump area. But check what these guys suggested first.

 

Have you checked for transmission leaks too? I had what I thought was an oil leak for the longest time, and it ended up being the transmission gasket and rear transmission seal (not main seal). Fixed both and it was spotless under there.

 

Mine appears to be sealed and completely dry so I can rule that out.

 

I sprayed engine degreaser (what I had left) on the underside of my jeep in areas I saw oil, let it sit for a minute then used my water hose and rinsed off everything I could.
This is my transmission pan. The bottom of it is dry and clean, no signs of fluid but the top left corner (the white looking bolt) looked to have some oil in that area. Not sure if it's just residual that didn't get rinsed off or if it's a plausible leak spot.

 

I did notice that after rinsing off the underside of my XJ with the water hose and allowing it to dry for a few hours, my oil pan plug bolt is allowing oil to leak. I'll be replacing that.