Farmall Cub

When I got the 300 it went into service right away as a mower cause the Cub was down. Since the Cub is up and running again I'll have some time to go in and do some stuff. What seals should I replace? Do notice oil dripping off the motor more so on the left side. Could this be to the fact that I added 15x40 Diesel oil thus I loosened up some crud? Also I have puddles towards the back of the engine compartment, not exactly sure what it is, however this just showed up during the winter so may be due to that. Still works fine just getting preventative stuff lined up.

Suggestions?

Have not had any dealings with a 350, but quite a few with N H. If the oil leak on the left side is toward the front, look the governor housing over good, as well as the front engine cover. As to the ones toward the rear of the engine compartment, could be rear main seal, or of further back toward transmission could be input seal. There is a pocket above that seal that catches oil and drains it down to the bearing, if that is the problem it will leak for a while after shutdown.