well, I thought what the hell, stripped interior out of helmet, then poured boiling hot water on the seal, which softened the glue and I was able to remove it, spent a couple of days working a rubber lube into the strip, then cleaned and re glued it back again.
IT DOES NOT LEAK and seems to seal well now, I suspect the rubber had started to go hard.
At least my old lid has a bit more life left in it now. (also got a new visor which is great as does not mist up like the old one)