This is the same Jawa you looked over - I bought it the next weekend. As for having sat for a long time, I'm sure it did. I'm just not sure when. I thought that Chad had been able to run it the year before, but am probably mistaken. He thought it was a two speed, and would go 40mph, but that's not the case. The speedo goes to 40...
Regarding transmissions - the tranny case was cast and marked for the 2-speed, but never machined for the fill/drain holes. Is there a gearcase and lube involved with a single speed set-up? If so, I can't find any evidence of them.
I don't think I have any front-side air leaks. The airbox pulls air up through a rectangular tube mounted to the upshaft of the frame, through the mease-ly scotchbrite-looking filter, into a chamber in the frame itself (!), out through a bit of rubber hose and into the plastic airbox cover on the front of the carb. Everything is sound and in place - I even fashioned a gasket for where the airbox cover meets the carb, to eliminate air leaks there.
Anyway, since I am unable to check for leaking crank seals, it sounds as though a trip to ScoBroMoCo/BlueCat may be the best route...
Thanks for all the input!