I have the exact same problem and thoughts on this problem, seems to be a volume of oil issue since its intermittent, and leaking from starters that have been recently replaced, I think its up to us to find a solution and post it, to put this evasive annoying problem to bed, any further recommendations ,from anyone with experience with this problem,I am going after the scavenger
tube area myself

Thank you for your reply Kevin
Yes it does have a wet bellhousing and the gasket between the starter and the bellhousing is sealed good no leaks there. And i agree with you it is probably the seal in the starter. But it seams to me the oil level is way to high in the bell housing. The lubracation for the chain is sprayed on to it via return line from steering so to me no real need to have 6 (that is an arbitrary number I do not know what the real depth is) inches of oil in the bottom of the bellhousing. And i know a seal is a seal but is the starter really designed to run submerged in oil? One thing I do notice is that there is no check valve in the return line so what ever is in the line when the engine is turned off will flow back into the bellhousing causing the level to rise to some extent. Since it does not appear to leak while running only after being shut off is it possible that is what is causing the problem? If so is there anyway to adjust the jet pump lower to compensate for the drain of the return oil?
Thank you again for any help replacing the unit is not in the budget any time in the near future.

Truck has a wet bellhousing so more than likely the seal in the starter is bad...there should also be a gasket between the starter and bellhousing....

I should add the oil is not leaking at the mounting flange of the starter but on the back side where the winding's are