Sounds like, maybe, the safety was already broken or cracked. Was it the main shaft of the safety that broke? Possibly a defective part.
Any 1911 full strip instructions should cover the thumb safety - but I agree it ought to go to Kimber.
You could cut the plastic into the profile of the grip safety, including the hole, and let the pin hold I in place. The trim it to remain inside the frame. Even if it's not thick enough, it could stop the metal-on-metal.
I have this kind of problem with a RIA, but used it for a carbine so I...