Passat 2005 Running On Used Soy Oil And B100

Today I found a spot of motor oil on my driveway. It's been 4k miles since my last oil change (I've been using the ELF brand) and so I brought it into Dan to do an oil change and check to see if we could see where the leak was. Oil pan and screw were clean. It's very hard to tell but Dan thinks its coming from the back engine seal. Not a good thing because it's like 8 hours of work to get to it and replace it. The car has 20K miles so it's not normal for an engine seal to be leaking already. Unless maybe that engine seal happens to be rubber and the owner uses bio diesel but who knows. So in Jan 06 Dan's going to replace the seal. Now some of you out there might suggest filling the car up with Diesel and trying to get this covered by the warranty and I've thought about it. But Dan can do this job in a day. The dealer is most likely going to take longer plus there's a chance that if the bio diesel did cause the problem then for sure it won't be covered and I'll have to pay dealer prices to put it back together again. The safest reliable bet is to have Dan do the work.