What he said^^
My ram balls were severely squashing and I could never get the mirror balls gripped tight enough- I did the same 'alteration' as Ghost,
I see he came out with something exact like 16.4mm and 16.7mm for each dowel. I just did mine by fit and feel, and just measured them now, and it seems to have come out with 16mm both sides, and going a little shorter would be fine IMO because as we already know the ram balls squash and it will just self adjust that way.
I just used a bit of aluminium for the dowel- I knocked the steel centre out of some big long fat pop rivets, cut the rivet head off, filed it to fit. You could use anything- I didn't want rust leaking out from steel, and didn't have anything in stainless that fit well, so aluminium went in and it works fine. The ends have dented a little bit from the pressure but they seem to be holding up and replacing them if I ever need to will be just as easy as putting them in in the first place.
It was a 5 minute job and they are completely firm and I can really clamp down on the mirror ball now and get things as firm as I would like. I highly recommend trying this super easy and effective fix before most of the other methods (scorring the mirror ball, dipping in stuff, etc). It really works.
I should note I had already read of this issue in this thread before I bought mine, that simple fix stuck in my mind, so was prepared to deal with it if/when required.
Great mirrors Ned