Did you mean Ultra Black, or just Black? The black's are normally for repairing weatherstripping and the like, so stay away from those in this case.
Both are highly oil reisistant as well as sensor safe.
The red is for continous high temp use, not sensor safe, and not as oil resistant as the Ultra's.
I believe the difference between Ultra Black and Ultra Blue is that Ultra Blue is supposed to work better to bond to surfaces that are not completely clean of oil.
I've used both, as well as the red over the years for all sorts of gasket making and never had an isssue with leaks.
As long as you clean the flanges really well, use either one.
Last edited by ramjamhemi; 04-13-2011 at 04:03 PM.