While I probably haven't shot as many arrows through mine as Dan has (probably about a 100 or a little more) I haven't seen any deterioration of my SOS rubber element. A friend is having about 20 bow hunters over to his place this weekend for some target shooting, socializing with other hunters and eats. I hope to put several more shots through the bow while I'm there. If there's any new developments with my TRG/SOS I'll definitely post them here.
One thing I did different than Dan was to install the TRG in such a position that I was able to attach the SOS so the string is just barely applying pressure. I've even pulled the rubber element off a couple of times to check for any tearing, stretching or any other wear and so far it looks like it did when I first installed it. I also haven't seen any cable wear from the TRG either. So, as best I can tell right now this system is working quite well on my bow. I don't know if adjusting your SOS like mine would make any difference with your setup or not but it might be worth a try. I hope you figure out why your SOS rubber isn't lasting any longer than it is.
2008 Martin Firecat Pro-X (29" DL, 66# DW), home-made TRG, new VEMs, DS Advantage/HHA Pro-5519 front sight, No-Peep Sight Eliminator, Limb-Driver arrow rest, B-Stinger stabilizer/dampener, custom upper STS, G5 Head-Loc quiver on custom mounting bracket. Gold Tip Velocity XT300 arrows with Bi-Delta 2.5" Sharkstooth vanes and Grizzly single-bevel broadheads, 498 grains at 262 fps (22% FOC)