I had a similar occurrence with 54mm two grain J280. The flight was successful. When I went to clean out the casing the motor remnants were fused to the inside of the casing. After much careful but forceful coaxing, the liner came out, but part of it remained stuck to the casing. A soak overnight in soapy water enabled the complete cleanup, but revealed a slightly discolored and slightly raised area the size of a kidney bean on the case. This was at the aft grain, not the forward closure. My vendor suggested not using it anymore, we took pictures (at the next launch) and submitted the claim the CTI, and they approved it. It took until the beginning of this season to get the replacement casing, so about ten months. Anecdotally, there were two other CTI casing claims filed at the same time as mine, both were 5 and 6 grain 38mm casings that had completely burned through and taken the fin cans with them, so these also were aft-end burn-throughs. Bottom line - the old case I have is not in bad shape, but people with more experience than me agreed it should not be used again. Why risk $300-$400 worth of rocket on a $60 case?