One of these days I swear I'll run into something easy that turns out easy. The replacement shaft arrived, but it won't fully insert. It'll go until the cover is maybe 3/8" from seated, and then just stick. I can turn the shaft by hand, and hear gears turning. Shaft doesn't look to be keyed, but I tried rotating it a bit at a time, and still can't get it further in. Any tips and/or steps I'm missing?