I had an oil leak from under the engine on a Mk 1 that I owned. It was under warranty and the dealer suggested that it was a crankshaft oil seal but on examining the problem realised that it was coming from the sump oil seal.This seal is a black one that fits in a groove in the sump.
They changed the seal but a few miles later the leak returned so they replaced the seal again only for the leak to return a few miles later.
I asked if, when the seal was changed, they used gasket cement. I was told that because of the design of the seal it didn't need it but they had never come across this problem before.
My response was that the leak was still there so what are you going to do about it? They changed the seal again but this time used gasket cement as well and lo and behold the leak stopped.
Vic.