Not quite a belt oddness, but....
Last year when I changed engines in the D I S C O, after I had changed the timing belt, I used the timing chest cover off my previous engine (newer and cleaner) and fitted a new water pump. All back together fine and dandy. Except a slight weep at the top of the pump mating face. Annoying but no biggie.
Bought another gasket - checked everything was spotless. Weep still there
Bought another gasket, took it apart, true'd everything, shiny clean. New pot of Heltite. Weep still there.
Swapped timing chest cover, bought new pump (neither were Britpart), true'd everything, payen gasket. Weep still there
In exasperation took the vehicle down to our local garage. Real world mechanics, lots of experience, work on a lot of older stuff, also sell fuel. They true'd the timing chest, cover and pump, fitted everything and it leaked. This annoyed them, so they made a gasket from the cork sheet that they make gaskets for the fuel pumps. No leak in 10K