Back in the eighties I rode my 400-4 for years with the adjuster bolt snapped off in the hole and an ezy-out snapped off inside the broken adjuster bolt (it was like that when I bought it). I had to order a new adjuster bolt and lock nut, split the cases and got the bolt disintegrated out. My horse shoe pivot/hinge did get damaged quite a bit from running with a lose chain for so long but it was still movable.
I always had to push hardish on the phillips head to get the rod to move - but it would always easily loosen if I reduced the amount of push - important not to push so much that it slows down the idling engine, you want the rattle to only just barely go quiet, no tighter!
John