ORIGINAL: tggilkey
The last several 60 size pattern planes I built used Spring Air retracts and just used plain old air and a hand pump. That seemed to work well -- the gear went up and down, had no maintenance to speak of, no replacement of supplies, and the medium used was free (except for some elbow grease). Have you tried air?
I have an air pump as well. I just recall that the Freon worked well and would last all day with one charge.