I'd like to hear from those of you who have used a filler on your valve covers to even things out or to cover welds that you don't want to smooth-out completely. I'm dealing with sheet aluminum (fabricated) valve covers which will make thermal expansion even more of an issue (the expansion difference between the filler and the aluminum is a concern).

I know about Lab Metal as a high-end, high temperature solution but what about fillers with glass added, or even regular bondo type filler over urethane primer in this application?

Thanks much, EM