Seeking help figuring out an oil leak.
History:  Had my local mechanic [competent and ethical]  pull the transmission last year so Daryl could install a LSD for improved traction. My mechanic replaced the rear seals at that time and put everything back together.  Six months later I notice a significant oil leak which drips down where the engine and transmission join.  I tell him about it and he says bring it in.  He drops the trany and replaces the seal.  
When I pick it up he says no charge.  "I was the last one in there."    Today, one month later I had to go back to the shop and tell him it has been leaking since I got it.  I asked him if he wanted me to take it to a Vanagon mechanic.  He still feels responsible but ask me to post the question to you all if there are any suggestions as to what is going on here.  I mentioned I thought I had read on here something about high case pressure.   What is the test for that?  Compression?  This is a high mileage engine, but it's a strong runner and normally doesn't use much oil. He checked the end play and said it was ok.
Thanks
Doug E.
'84  Van-Go
'67 vw convertible  Vert-i-go