transmission seal leak?  Are you sure that it is engine oil?  Are there galley plugs on the back of your engine type?  These are pipe thread plugs and they can leak down right on to the rear main seal area.  You would need to have the block plate off to see if this is happening.  If you have had the flywheel and block plate off to do your seal replacements you probably would have seen any leaks.  But, if the block plate was left on you wouldn't have seen the back of the block.  There is also a cam plug back there that can leak if improperly installed or if it was not sealed.  This is where the oil from a rear intake leak can also drip down - tightening the intake bolts won't stop an existing leak at the back of the intake.  You are probably tired of this area being mentioned but it is very common and often only reveals itself in the bell housing.  Are you running PCV?  If the top of the engine is buttoned up too tight the crankcase pressure will look for the path of least resistance which could be a crank seal.  Most lip seals have fairly low sump pressure limit.

Another posibility is the condition of the crank sealing surface.  The surface finish must be quite good and it is essential to ensure that there is no "lead" in the surface.  If anyone has attempted to clean up the seal surface with sand paper, for example, you can develop a lead in the surface which can cause the oil to be pumped out under the seal.  There is a shaft lead test kit that can be used to check a seal surface but that's when the crank is out.  There is no real repair to the actual crank seal surface without plunge grinding and if the size is on the low side there may not be enough material to remove to clean it up.  You can't see shaft lead but if the crank has been reground or refurbished it may be compromised.  The solution to shaft lead or a damaged seal surface is a product like speedi-sleeve.  These are available for most cranks.  They are a think stainless sleeve that is slid over the seal surface with a special installation tool.  The installation is a little tricky but if properly installed you will have a fresh and proper seal surface.  The added OD is within the limits of the rear main seal.  This repair is only needed if you confirm that you indeed have a RMS leak and if the crank seal surface is compromised.  Here is a link to a picture showing the traditional method of testing shaft lead (also called threading) - http://articles.sae.org/10515/  Lead actually can cause oil to be pumped back into the sump which causes the seal lips to dry out and fail.  If lead (think of right and left-hand threads) is the oposite direction, the seal acts like a pump.  When the shaft isn't turning it won't leak a drop but in rotation it pumps.

So after all that, is shaft lead the problem with your engine?  Not sure - but you need to look at all possibilities and knock them off the list one by one.  If you don't know the history of the crank or if it has been ground there is a chance that the seal surface is compromised.

If you do get a speedi-sleeve to repair the crank after elminating all other potential sources, contact me and I can review the installation process with you.

Last edited by GPatrick (4/26/2014 9:00 PM)

edited my post - hit the button too early the first time.  Take a look - and there are a few other things I can check from the seal side if none of those suggestions/ideas pan out.

Thanks for the info GPatrick.   Its leaking slightly.  So with a short driving season I think Ill deal with it and pull the transmission this winter and take a look.    I also a 5.0 Engine that I might replace the 302 with.  Ill keep an eye on it and check the oil frequently.

Thanks
Steve69