the lugs are 0.7mm thick on the right side and 0.95 on the left (at least on the Elmar on which I am working now). Although hard to believe that the lug could be broken on camera hit (other damages would be much more visible), who knows. Anyhow, due to increasing thickness you should be able to fix the lense if turn enough when locking. You should have no play forward-back. You might possibly have some play up-down due to missing lug, but this should be compensated with new, maybe slightly thicket velvet.
Inserting the barrel into focusing mount is always tricky. Therefore i made a tool for myself, see foto. On one side it goes into barrel, the other side is smaller in diameter and this is where the focusing mount is pushed onto.