Tuning Rebuilding older Steyr air cylinders???

Thanks guys. Mine is a pcp. Truth be told Pilk won't work on these because they are past the service life limit. But for years these cylinders didn't have any air in them because they leaked out overnight, and before that were rarely stored more than half full.

I looked at my original receipt yesterday and I bought this gun in 1999, a long time ago.

I should see if Steyr could advise me.