JDL,
mine was completely stuck at first too. I ended up removing the vent and the linkage separately. I was only able to free up the handle on the shop floor by using a propane torch. Now of course the whole thing works properly, detents and all. I used brass bolts and nuts to assemble it to avoid problems in the future.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!