I have a '74 CL125 and the heat shield over the header and muffler rattles a good deal when the revs are high. This is due to a gap (5mm or so) at the little bracket where the shield mounts to the header. Is it ok to put some rubber in there as a shim? I'm worried that rubber would melt due to the heat. Anyways, just curious if there is something that you're supposed to use. Thanks.