Left my Craftsman tiller model #917.296040 in neutral over winter. Now it won't shift into any other position. Have engaged the drive bar (not in gear so it does nothing) and tried "rocking" it (not in gear, so it just rolls). Have sprayed the shift rod where it enters the transmission case, in case it had rusted. Nothing.

Hi,
The manual is here:
http://www.managemylife.com/mmh/lis_pdf/OWNM/L0601150.pdf
And it suggests rocking while trying to engage. Page 47 shows the parts breakdown an I might suggest tapping on part# 13 with a hammer on the edge of the flat part if it is visible. You might also try it move the tines a partial rotation with a pipe wrench to see if that helps.
Peace,
Clarke