The TAG and the TOG before that used to be 'the' resource for these guns, but membership and posting has died off some.
There are still some of us from the old days who hang out here and on other forums who may be able to help.
First thing is to find out where the leak is. Use a q tip with some soapy water. Likely going to be getting bubbles from the tophat, or the brass ring under the tophat and possibly from the burst disc or main valve body.
For seals, can get rebuild kits just about anywhere. Once you dive into them, they really are not hard to reseal at all. Biggest issue is having the proper tools to remove the valve so that you don't mark it up.
Figure out where the leak is and give me a holler on PM.