Well, this is the process of elimination, right? So a poopy result has a certain poetic justice to it. ;-)
Backwards is effortless. Frontwards I get the click. During reassembly, with the mower on its side, if I spun the blade the rear wheels would move.
I have not the slightest idea of what's in that transmission or how one works. Is it possible that there are no teeth left on the gears in there and it is truly worn out?
The spring always goes on with a bit of a bang, but I didn't see any obvious carnage as a result.
Unless I hear otherwise, I'll order a new transmission tonight or tomorrow. I don't think it could "only" be a stretched cable, but I'll order a new cable to go with the transmission.
I appreciate all the help. Now if a new tranny doesn't fix it, then I don't know what I'm going to do (yes I do - I'll need a new mower!). Thanks!