Thankyou for the advice.
I'll renew the seals before using and take your advice David to roll it tight on completion and as I'm taking about 130 rolls of various films I think I'm just going to let it run the gauntlet of the Xray machine and suck it and see.
(I had a bad experience at Singapore once with a lot of film and nearly missed my flight!)
I have two backs and one has a large diameter leading roller and the other a small dia. like the 120. Is it possible this is just an early and later model?