Many yrs ago I didn't like to have to pump them up all day if we flew many flights, so I filled them with freon, and one fill would last about 10-12 times, but would only fly 5-6 times before adding more. Just add someoil to itevery other fill.It regenerates it's self. I haven't had anything with retracks since then, but I have 3 sets now and going to build something for them.

Pat