flex plate keep's cracking

i was coming back from a car meet, and flex plate cracked got it home, than bought a 2nd hand 1 that wasnt 100% straight, i didnt notice till i got it home and was fitting it, i fitted it and was driving about in it and it cracked again

my thought is.

when they took the original 273 and put the 318 they must of wrested the flex plate on something and it weakend it. as the previous owner did very few miles and never took it on motorway. and when i put the 2nd flex plate in, it wasnt 100% straight so i must of weakend it when bolting it back up.

there is no vibration on the box what so ever, never slips gears etc.

am i talkin aload of rubbish here, or could this of being why they cracked.

i have bought a new flex plate, so if this cracks again i no there is deffo something wrong with the box.

cheers