I can't even begin to tell you how f-ing annoyed I was getting by the slippage on my GS1ks...Martin's rodblocks were the ticket and it's really been a great investment. Some likely will consider them pricey, and I can't disagree, but it was a very worthwhile purchase for me.
I came across the same problem with my MS2i's and read some post's on how people would crazy glue the rod to the rod blocks, wich I could not believe what I was reading! So I went to my local hobby store and purchased what are called (collars) in a nice chrome finish with set screw's in them along with some rubber O-rings, placing the O-ring onto the top of the rod's first to protect the plastic rod block's from the metal coller's, then sliding the collar on top of the O-ring and locking them to my adjustment with the set screw's and they could not have worked out better. I too was considering the martins rod blocks but they were too pricey for me, and that would have lead me to more and more custom upgrades and would have got very expensive (just about the price of my headphone's) and could not justify spending that much on cosmetic's but I wish I could have. Good for you, enjoy!