RE: New old Jett motors. Bob? what is this?
The first and second photos looks like an early to mid 90's motor from the case and carb design (low-end adjustment have needle for adjustment vs. newer version fit flush). The third photo is probably late 90's to early 2000 from the new improved cast case based on the bump on the bottom. I think that's what it looks like, but Bob can confirm that.
The gunky and leaky head is a sign of worned out motor either from owner didn't tighten the head screws properly and caused a leak or onwer didn't really take good care of it. Jett engines should not have a leaky heads from my experience from all that I've owned. They all looks brand new with everyone I have. Just a thought!