I have taken on the responsibility of cleaning and preparing our schools horns for the upcoming marching band season. My question is: What do I use to lossen up stuck valve caps and slides? I know to take a towel and loop it through a slide to gently remove those, but what is the best way to loosen valve caps? Can I use a penetrating oil like WD-40 or would a pair of pliers be better. I don't want to cause any damage to the horns, but I know some of them haven't seen the light of day for a few years. Thanks for your responces.