Good to see someone else is still using a GTS2M! (I use mine as my backup OH cube). I wouldn't think that DNM-37 slows it down, if anything, the more you add, the faster it gets. However, you only really need 1-2 drops, so if you added any more than that, it might be overkill. If you didn't, I would imagine some other cause, like dust that's been kicked up, would be the problem.
Either way, I would recommend cleaning it out with a paper towel, and make sure to get into the torpedoes. That should fix your issues. If it persists, try cleaning out the screws and springs, as those can get a bit gummed up too.
This was an entirely unnecessary and useless post to this thread. Please think before you post. You're 54, for God's sake. You should know better.