I recently purchased a PMR and changed the End Cap to the alloy one. The O-Ring on the inside of the bold that attached to the end cap came off and I cannot get it back in and the O-ring looks like it was worn by my attempts to install the alloy end cap. What is the size of the O-ring that goes on the inside of the back of the bolt where it holds the end cap. I have attached a picture to illustrate the location of the o-ring.
