Since one cam lined up at TDC but the other didn't, have you considered the possibility the chain has been changed but the timing wasn't done correctly?

10 degrees sounds pretty close to being one tooth off. The right hand cam, I believe, has the long chain run and is where the tensioner is. THAT would be the first place stretch should show. Check the chain for a replacement link.

Somewhere in the dusty recesses of my mind there's an abstract nagging memory regarding the M116 engines and timing marks but I just cant dredge it up.