1st cylinder I got no pieces bigger than about 5mm, (using CRC).
2nd cylinder I pulled off a few pieces about 25mm, (using brake cleaner).

It's possible that the gasket on my 2nd cylinder just wasn't stuck on as stubbornly as the first one, but either way, job's done and my barrels are back on.
I'll post up some pics later - right now, I want to get back into the shed and fit my new Tyga pipes!