Sounds like you have the Vauxhall Race Damper. Much beefier than the standard damper and valved specifically for the VX Caterham (or so i was told).
I'd stick with them and get them re-built.
Google came up with:
KBSS Ltd, Unit 3, Swannington Road, Broughton Abbey, Leicestershire, LE9 6TU. Tel:01455283407