Hello Bob...thanks for the reply. After some looking, I see that they use deadsoft aluminum on a lot of collector and header gaskets. Also copper in a deadsoft form is used. My builder had mentioned along time ago something about sheet copper that had been softened.
Anyway heres a neat link to sealant properties. They have goofed on the RTV grey tem at 700 deg F its actually 625
http://alphasourceintl.com/seal/sealant_properties.htm
But neat to compare. The temp limit on Ultracopper at 700 deg F
Doesn't that seem low still for exhaust temps? I would expect the collector flange to be pretty warm
Tim