Well, back from a week's vacation, with success to report!
First, FluffyChicken, I've seen O-ring problems with my fork in the past too: Mine has long been hard on the O-rings that are installed above and below the bushings. After a season or 2, these rings tend to need to be replaced. The symptoms of their failure are hydraulic-locking of the fork after a big hit. The fork simply fails to rebound until it's re-compressed, then it usually comes back. $2 of new orings and an hour's work sorts it each time.
Back to the needle valves:
I had moulding problems with my first attempt at moulding the needle valves with the hole partially pre-cast. It made getting a good mould fill difficult and the wax slowed the curing down to glacial rates. Only 1 of the 4 pieces i moulded was good enough to want to use. I tried it, and it worked!
I'll describe exactly what I did, so the next guy might find the info easily:
I made a maple mould with four 8mm holes drilled thru it. The wood was about 3/4" thick. I drilled slowly to produce as smooth sided holes as I could.
I chose Permatex Ultra Black RTV sealant, on the basis of its claimed resistance to oils.
I used a toothpick to smear a thin coating of vaseline inside the wooden mould. I removed the tip from the RTV tube, and carefully filled each mould chamber, from the bottom up, ensuring no air bubbles were included. I covered the ends of the mould with strips of newspaper, and set the mould aside for 3 days.
When it came time to eject the plugs from the mould, I chucked a deck screw into my bench vice. Happily, its head diameter matches the holes well. The plugs pressed out with easy force. Squeezing each plug between fingers would reveal its quality, air holes showing as soft spots. I only needed about 10mm of each plug for my valves (the originals are 10mm long), so I chose the best segment of each valve, and trimmed the ends with a razor sharp knife.
Now I needed to puncture the needle hole thru each valve, and I chose to do this before installing them in my fork. I took a 15ga spoke, and cut off the head. I chucked it in my drill, and spun it against the side of my bench grinder's wheel until an acute point was formed. I had noted that the original needle valves used a 3-sided puncture, so I refined the point to a triangular one on a whet stone. Finally, I pushed the needle thru the middle of each valve piece. It went thru easily and cut a nice 3-sided pattern, smaller but not unlike the original valves.
Inserting the new valve in the fork air caps was easy enough, just poke'em in. They're retained by the adjuster rod tops upon assembly.
Once assembled, I lubed the tip of my inflator needle with grease, inserted it and easily inflated each leg to the 44 pounds I prefer to ride it at in these, my heavier years. Each valve sealed quickly and surely upon needle removal.
Thanks for the tips, guys, you were spot on!
FluffyChicken, I need about a 180mm steerer for the wife's bike. She just made the jump to clipless peddles this past week, however, so the bike budget is shot for a couple months.... LOL.