Hey Mr. Westfield - I'm also a relatively new owner of an FXRT (1984) - I bought it late last summer. I'm no expert with these models, but I am also having trouble with losing air in the fork system. Here is a reply I got on the Yahoo Groups FXRTouring group:
"If you have not changed the fork oil you don't really know if you have any oil in that side of the fork. The oil level is the only thing that keeps the air pressure in your front end. I don't know how long you have had this bike but if not too long, it may have had a leaking seal when you bought it. I used to pressure my 84 FXRT forks to maximum pressure when I first bought it because the front end was just too soft. I hit a railroad track one day and blew a fork seal. When I tore the forks down to replace the bad seal I installed Progressive springs. That was the single best improvement that I made to my FXRT. You won't need to pressure your forks up as much with the stiffer springs. Another thing you need to check is the diaphram in the accumulator. I've had to replace my accumulator because the diaphram was bad. It's just a sheet of rubber in the accumulator. With zero pressure on the forks, pressure up the accumulator and see if the pressure holds. If the accumulator pressure drops and the fork pressure goes up, you have a bad diaphram. I installed an air pressure gauge on the fork air tubing to oversee the fork pressure. A zero to 30 pound gauge is too small a range because the fork pressure will go higher than 30 when you hit a bump and screw up the gauge. You have to use a zero to 80 pound gauge about one inch in overall diameter to clear the fairing. It sounds like to me that you have lost the oil in one fork leg and that is where your losing air pressure. Remember that the fork oil is the only thing that is holding the air in if you don't have any other air leaks."
Important thing to note here is that the diaphragm in the accumulator could be a second source of leakage. I just received my parts to rebuild the forks with new seals, and after that I will perform the accumulator test to see if that is leaking too. I think it would be pointless to test that while my forks are still leaking air, as I might not see the fork pressure rise as the accumulator pressure lowers.
By the way, check out that group I mentioned above.
http://autos.groups.yahoo.com/group/FXRTOURING/
It's dedicated specifically to FXRT/FXRD/FXRP owners and fans. Really great group of guys there.
Ride safe and have fun
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