those starters are pretty tough, the main thing that fails on them is the end bearings [bushings], which are probably tightening up from the heat and loading it down - I wouldn't worry about ruining it, just give it a half hour to cool off and it'll be good to go again - use'em til they break
if you do get the heat shield on and the problem persists, it'll be those bushings worn right out, easy enough to replace, been thru that myself
Bill
