I didn't want to slather mine in tar (Blackjack) although I do understand they also sell a butyl caulk.
Being in the building trades I always seem to have a half tube of urethane or polysulfide caulk around.
If it's good enough to seal through hull fittings, I figure it's never coming off the cowl.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.