any time I have my bell off and accessible I clean it off with acetone, or denatured alcohol. don't drench it, just clean it real good to get the sheen off of it.
you can break clutches by "poppin" the throttle or "flipping" the throttle on the way to the flight line actually. you know, rev rev rev rev, that is not good on one. you can also damage them in a crash like you mentioned. just think the stress that shoe has on it.