"some of the best sounding cymbals Ive ever heard where cracked ..
as strange as that sounds it true"

oh that's blasphemy, jk.
i can hear a crack in my cymbal almost the hit after I crack it. i've even predetermined a crack from how it was sounding. I can't stand the sound of a cracked cymbal. i don't use my cymbals alot, I'm more of a batter drummer. but when i use them i expect exactly what i chose that cymbal for.

I've tried everything to mend or stop a crack. From drilling at rhe front of a crack to chopping a cymbals diameter to below the crack on a lathe. ( I used to work as a machinist). And there's something about the integrity of the material in the cracks path that has already fissured and the crack is just follwing this weakened line.
if the crack is transecting the gong from the edge in, try using a propane/oxy or oxy/acetaline torch to heat the metal around the crack to a dull red and then slowly over 5 minutes or so drop the heat from the torch and then let it cool slow. This will anneal the metal reducing it's brittleness, then drill a small hole at the front edge of the crack. The gong is gonna oxidize were you heat it and turn blackish brown and it won't polish out. This MIGHT work for a little while. And depending on the size of the gong while change it's sound and resonance

good luck and let us know how it goes