I did a search on can borers and that's how I found your thread. I have lots of cane borer damage this year. I bought a new glue by Elmer's but it's polyutherene. It really seals. I had to cut some of my established roses down to 12-14 inches.

Carla

Cane borers also bore in from the side. I've found sealing the ends a useless and thankless and labor intensive task that I no longer bother with. THe damage is no better or worse than when I sealed.