You found the problem by taking it to bits and investigating. Well done. The internet is a good sounding board and can give you a heads up as to where the problem may lie, but you can't beat hands on and good old looking. The puller did the job and the damage was caused by inappropriate use. Protecting the threaded hole with a bolt or a plate would be the way to go. We learn by our mistakes is all I was saying and keeping your wits about you and your eyes open can help to not cause more problems as you go along. We've all done it. If it's only the first five turns that are damaged it might be possible to drill out the end of the hole where it's damaged. It depends on how long the bolt is that's going in there and if there's enough thread left to hold it all together .