Ah yes Tim, I remember having this problem with almost ALL my old Naish struts. I tried EVERYTHING under the sun, but nothing ever held more the one session.
Here's a few things that you may try:
http://www.kitefix.com/support.asp?lg=en&sct=rep Look for Valve base repair
http://airtimekite.com/valve_page_1.html These work VERY well!