On a Wheeler Dealer episode (Saab's your uncle) Mike takes the cylinders from the Saab's top to "Top Hydraulics" and they show you how he repairs them. It involves a lathe to "part off" the old seal housing, and if I remember correctly they use a special seal housing manufactured for Top Hydraulics themselves, to renew the seal. Not sure it is something you could actually do yourself, but best of luck. I am of course assuming that the cylinders on the Saab are similar to those on the Crossfire.