For years, I had used Felco bond with fantastic results. Sadly, it was. Discontinued a few years ago.
Since then, I have used Permatex #1, as well as standard RTV, each with no leaking or comebacks.
Damn, I really miss that Felcobond.
Well I have a pair of '87 360 truck manifolds and your more than welcome to, at no cost. You have to come pick them up, but I am in Woodbridge, about 25 minutes from you.