17LP4 CRT ( Need one... )

[Phil Nelson]

If grimer has a good tube for you, that seems better all around than trying to seal a big crack.

There is an expensive product called Vacseal. Some folks apply it on the leak-prone parts of 15GP22 tubes on the theory that it can't hurt and might help prevent future leaks.

http://www.2spi.com/catalog/vac/vacleak.shtml

Even if you seal that crack, I'd be concerned that heating & cooling during normal operation could make the whole thing go PLINK at any time. Once a crack starts, the weakness may put stresses on the rest of the neck.

Phil Nelson