Recently was given this sled from a friend and first off had issues with the original carb (keihen) so changed it out to a Mikuni VM34. Would not fire unless i removed spark plug and put some gas in. Took the sled out for a run and it ran for about 10 minutes and then began to bog and then quit. Now noticed that there is oil/gas spray on the hood and below the engine. I think it is coming from the crank seals. Just wondering how much work it is to change them out and what all it entails? Any help would be great.