I am looking at a 2004 RM125 that has a plug fouling issue. The owner said the top end was rebuilt and about 2 riding hours later it began fouling plugs nonstop. He said he took it to a shop and they told him that the shop said the gasket between the crankcases is leaking. My question is: what would cause this to leak? He told me the bottom end has never been apart. He also said that there are no cranks in the cases and its not blown up. How likely is it that the gasket is the problem? Sounds like a crank seal to me. If not what else could it be? Think he is lying about the shop? If I go check out the bike, what should I look for? Anything I can do to ensure the bottom end isnt toasted? Thanks in advance!