I just chased down a oil leak on my 93 maristar. I thought it was the rear main seal leaking because it was dripping down the bell housing. It ended up being a small pinhole leak in the block about an 1" from the drain petcock. At idle or even up to 1500 rpm's it wouldn't leak, but around 2000-2500 oil would start coming out of the hole, run down the oil pan gasket and down the bell housing.
Yours sounds like it is in a different location than mine, but it is worth taking a look at. Best thing I did was take the motor cover off and have my wife drive while I crawled around looking at the motor. I never would have found this if I hadn't had the motor cover off and if we weren't above 2000rpms.
You might be able to search for the thread I started. I included a picture, which might be helpful.