Ive just been to the ironmongers and bought two new
fibre gaskets. They seem far more chunky than the supplied effort.
Will go for ptfe tape on the thread and one of the new gaskets.
Hopefully that will sort it.

BTW I highly recommend the company I bought the cylinder
through they were IFS and are based on the South coast.

http://www.gasapplianceguide.co.uk/index.html

I ordered a new 160 litre Geldhill cylinder along with a diagram
showing the custom fittings I wanted on the cylinder and coil
type etc. The cost was significantly less than an off the shelf
make from my plumbers merchants to the tune of about £100
and it turned up in 3 days straight from Gledhills!

Might repost this as a seperate thread as other people may
be interested. It saved us a lot of money.

Matthew