I always apply FS before headset install (unless the frame came w/ headset, then tried to spray around it). If it's not installed, take advantage of that and hose the frame down! Then wait a day or two for the excess to dry/leak out before you continue. If they're chasing the BB threads, might as well have them install it at the same time.
Have them face the headtube surfaces while they're at it. Probably not a problem, but if you wanna' do it right, one thing to look at.
Have fun with the rest!!!
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Cheers,
David
Redlands, CA
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“The good thing about science is that it's true whether or not you believe in it.” ― Neil deGrasse Tyson.