base timing keeps advancing by itself...

Correct.. I have to move the distributor clockwise past the original marks to get it back down to 12 btdc. The spot I had marked as 10btdc cold was now corresponding to 22.

You might have something with vcan binding the advance plate. I don't see any indicators in the distributor that this is happening, moves freely through range of travel, but thats the only thing that makes sense so I will try to run it down.