Had my rear main seal replaced about a month ago and noticed recently oil dripping slightly from tranny cover. My mechanic checked it and said rear main isn't leaking and oil is just residual from when he replaced seal. Does this sound right ?

 

Check For loose valve cover bolts. The front of the engine sits a little higher than the rear thus leaking valve cover the oil runs down the back of the engine and fools some people into thinking its the rear main.

 

^ This.

Also, same goes for the oil filter adapter. The o-rings on the adapter could go bad, causing oil to drip down to that area and mimic a rear main seal leak.

Degrease the engine compartment, take it for a short drive and then take a look again and try and track down the leak. The upper most point is valve cover gasket. Then the oil filter adapter and oil pressure sending unit, which are also possible areas that it could be leaking from

 

My standard response to potential RMS leaks:

I'd be looking up above first. A leak at the back of the valve cover could produce the same symptoms. Don't jump on the RMS/oil pan gasket bandwagon just yet.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for 2 simple reasons. First off, the engine sits nose-up and oil will run back to that 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 have to be eliminated as possibilities first.
Revised 3-23-2012

 

Mechanic is probably full of ****. I chased all that other crap after doing my RMS and it still ended up being the RMS.

 

The oil is coming from under the bolts of the tranny cover

 

I don't doubt that. Valve cover leak can produce the same symptom. Check it out.

 

I've seen a few times after the RMS was replaced that there was still a leak. It ends up being the oil pan gasket wasn't put it right and leaked past it.

 

best thing i have ever done for oil pans is buy a 1/4" torque wrench that does inch pounds. if you get pans too tight or too loose they leak. the new style cherokee gasket isn't bad with the steel reinforced rubber but i'm still torquing to spec when i do mine. some cars like the 90s honda B series engines you almost HAVE to use a torque wrench. gaskets are solid rubber and squeeze out if too tight and leak if too loose.

if you want to be cheap harbor freight has a 1/4" torque wrench you can get on sale for 19.95 often. it's close enough for an oil pan. wouldn't trust it on something serious though

i've also sworn off rtv in favor of the right stuff. it just leaks less. can't explain why but i have fewer failures with the right stuff vs rtv.....actually i have never had a failure with the right stuff. with rtv i've had more than a few re-do's

 

My brothers -88MJ had an big oil leak. All the experts said that the RMS was gone and needed replacing. The same day I read cruiser54 suggestion about the valve cover gasket and told my brother to come over to my house and I would replace the gasket for him.
I took the valve cover of, cleaned it and replaced the gasket, and viola no more oil leak from the RMS. So always do the easy things first.

 

Did my RMS on my 200 its started leaking and i see oil trail on my filter i got the seals know im just procrastinating.

 

I can't begin to tell you how many times over the years that I've seen misdiagnosed RMSs. Most times there's a much simpler solution if you look at it yourself and not rely on some drama queen mechanic.

 

Spent $400 to replace rms. How much to replace valve cover gasket ?

 

Pay someone? Probably $100.

 

About 15 minutes and a 7/16 socket. Or is it 10mm i cant remember.

But it is one of the simplest thinks to do.