Did you try the epoxy seal method on either motor? Basically you run a bead of JB weld around the liner and the top of the top grain and then seat the forward closure with a twist to try and prevent blow by. It's been discussed in a number of posts about the long CTI motors. I think Jim Jarvis was the one who first figured it out. I've used it for several years now and have not had any failures, but I do know at least one flyer that had a burn through even after trying it.
I have been flying the 54mm 6XLs for years - primarily the L265 and L935, and the L640 when it was available. I have one each for the L265 and L935 on hand. I've also flown a fair number of the long 38mm motors - the J150 and J530 and also have one of each on hand. (I sense a pattern.) I've not had a failure but I've seen many of them personally, and of course have read the reports here as well. I know motors have been decertified in the past for safety issues if they failed enough, but then others, like the Estes E engines that I read a lot about, remain in service. I'm not sure what the right call here is but I feel like I'm sitting on a ticking time bomb, and it's only a matter of when, not if, I'll lose a rocket to a long CTI motor.
Once I use up what I have on hand, that's it until CTI figures something out. What kills me is the one Aerotech motor I flew as a substitute cato'd due to a cracked liner. I lost an Orangeburg 2000 LDRS case due to that.
I get rocket motors can have issues, but when an issue is as persistent as the failure mode of the longer CTI motors, it needs to be fixed, and sooner than later.
Tony