I apologize now to the rest of the world for the Imperial units used below...
I just abandoned the air-assist feature of my '79 CX500 forks last weekend. These were apparently an aftermarket setup, with one Schrader valve feeding two 1/8" tubes, one to each fork cap. The tubing fittings were a spring-loaded press-in type. The system would not hold air, even for a minute. I used soapy water on all of the fittings and could not find any leaks.
I'd submit that a leaking air setup wouldn't necessarily allow the air inside to compress with upward slider travel, making them even softer.
I used a couple of different size screws to hammer into the springy press-in part of the fittings on the fork caps to get them out; since the springy parts spin, drilling wouldn't have done anything. I then plugged the holes with JB Weld epoxy, and put a 3/4" long spacer made from 1/2" galvanized water pipe under the cap in each fork. I wish they had been a bit longer, since the Windjammer on the front adds a reasonable amount of weight and the tired stock springs are working harder than they otherwise would.
Just thinking about air assist, and guessing at an approximate 1 square inch of internal cross-sectional area of the fork tube, even 10 psi (and it was mentioned in another thread that 6-10 psi might be the proper range) would result in a preload of about 10 lb. I'd say that I pushed down with a lot more force than 10 lb. when I was re-installing the fork caps with those spacers, so I think the air assist isn't doing a whole lot unless your springs are already pretty close to the stiffness you need. At that point it might be good for fine tuning.