Originally Posted by
merziac
From there it takes a very light touch and anti seize to get compromised threads started, very hard to feel the first thread "catch" and know if its aligned perfectly without causing more damage as you found.
Go backwards - if a right-threaded cup, place it in the shell and turn anti-clockwise with light pressure. When the cup gets to a point it will drop inwards one thread and that's when you know you have the start.
For damaged threads there may be more than one point where the cup drops. Check the cup visually as most often the original threads will still be there, and hopefully they are still deeper and better formed than whatever damage there is. Go around several times and decide which point has the best-feeling drop - size, and at the moment after the drop look at the alignment. Use that.