Glad you got the leaking cylinder sorted.
I too have heard good reports about the Portsmouth Gun Centre, although I've never visited it myself. It's about the closest decent gun shop to me now, since Chaplins went, although Alex is still carrying out servicing and repairs.
I had a similar problem on the S200 cylinder used as a reservoir on my PCP Service rifle, and sent it to a well known member on here who re-sealed it in a very short space of time.