I've personally seen two TM V7 gearboxes that were cracked, but not where you'd expect. Both were cracked on the left side, about halfway down the cylinder area but just on the top. Neither appeared to affect the guns performance at the time. Neither client chose to replace the shell. I don't know what ever happened to them after they left my shop.
ASC & RAAT Age Verifier for Red Deer & Area Alberta