Jeep Repair: 91 cherokee oil leak, under drivers side only, transmission oil cooler, crankcase ventilation

Question
1991 jeep cherokee 4x4 4.0 v6. Everything under the car is coated in oil, but only on the drivers side. Whats leaking? it has 162,000 miles on it. thanks
-dave

Answer
Well... The 4.0L's were notorious for having rear main oil seals leaking.  This would develop at the bell-housing though and be dead center of the vehicle.

Crankcase ventilation orfices were frequently get neglected causing poor airflow through the valve cover and such.  This would lead to excessive pressure causing gaskets and seals to be blown out.  Oil caps leaked too.

The valve covers back then I beleive were RTV and would eventually fail, Cork was probably a worse gasket replacement than RTV too.

Oil filter adapter seals would leak and require not only a torx socket but alot of patience, wrist power and a speed ratchet like what gearwrench sells since a ratchet and most torx sockets won't fit.  That however is on the passenger side.

Next you've got the question of whether or not it's actually engine oil.  Front pinion seals would leak oil and that's on the driver's side.

Next is the steering gear and pump.  Both on the driver's side again.

Then finally you've got transmission oil cooler lines, provided it's automatic, that could leak.  Some people beleive in trans services and others don't.  Those that don't let the fluid get real nasty and instead of being red it turns brown in color.  

You'll have to determine the true color of the fluid and also degrease the engine to actually be able to tell where the leak is coming from.

I've pretty much named all of the leaks the 4.0L had but without degreasing the engine and rechecking daily if not more then I really couldn't tell you.
Doug