I'm assuming you're doing all this with either the track lifted off the ground, or the sled laying on it's side.
From your first post it sound's like you were running the chaincase without any lube, something could be siezed.
Those gear's should move freely in there, if they don't then you know where to start.
with the chaincase open, try moving the gear's in and out of reverse by hand.
Also check if anything is jammed up with the operating handle.
Both should move freely, if the gear's don't, you'll have to tear down the chaincase until you find what's jamming it up.
If the handle is jammed, you'll have to track it through the linkage's to the chaincase til you find the problem.
It's a fairly simple mechanical system, so it should'nt be all that hard to troubleshoot.
I know it suck's having to work outdoor's in cold weather,.
Don't let it get you down, you'll figure it out.
Rick