I use an EZ-out for removing damaged grip bushings. You first need to check and make sure that the bushings are not staked. I always heat them with a heat gun to soften any loctite that may have been used. In the future do not use a screwdriver to remove or install grip bushings. Buy the bushing driver bit from Midway or Brownells.
I just kind of have to laugh, because I did the same thing, on Christmas day last year, putting on my new Christmas present grips. One side came out easy. The other side, not so much. Just glad I had new bushings on hand.
eze-out or the red loctite trick. Bushings are expendable.. Put the new ones in with blue loctite and smooth out (clean) the threads of the screws real good. Oil the screws, wipe down and install. If they come loose, use washers.. It works for me.. Cheers.. Ron