VCR does everything except Play

[ESigma25]

I've been wrangling with a Sanyo Hi-Fi VCR (model VHR8310 for anyone curious) and after figuring out its weird mechanism timing, I've got it to ALMOST work...but the last problem is stumping me.

Tapes load and eject without issue, and both Fast Forward and Rewind work just fine...but Play does not? It makes an effort to play but the take-up reel doesn't start turning and the machine aborts playback. There aren't really very many timing marks to go off, is it possible that it's somehow still out of time even though most functions work fine? Or is there some other cause for the take-up reel not being triggered to start turning during playback?