I walked out to my garage to pull the donor MC from the parts washer. I went to put my gloves on and now they are almost 2 sizes bigger than 5 days ago. I mean, they are HUGE now. Grab the MC and try to do a hand held bench bleed with it. I can barely get the piston inside to budge. Apparently the question: "does mineral spirits used in a parts washer damage rubber seals?" is answered. If you consider making the seals almost twice thier size to be damage, then the answer is YES. I never imagined it would have this dramatic effect though. Now, did it damage the seals inside the brake combintion valve with 5 minutes of limited exposure? That answer will probably remain unanswered. I know I wont put any rubber anything near that stuff from now on though. Wow.