The only part besides the o ring that I have replaced on my 1100 is the interceptor latch retainer. Get the 3 pack from Brownells because it comes with varying thicknesses. I suggest going ahead and replacing it with the thickest one. The Brownells retainer seems stronger to me and should be less likely to remove itself from the gun in the middle of a stage. But once you get to the thickest, the gun is done. That boss is part of the receiver. Went thru two 1100's over the years. No more remmys.