I've been trying to use the madbull adapter and propane and it just wont fill.They most likely add it because it sounds like it should be a good idea, which doesnt neccessarily mean it is.
Speaking from experience of using dry propane, I very rarely get a leak, my MWS mags for example have never leaked in the past 3 years that I have owned them.
Occassionally when a mag develops a leak which is a very rare occurance, I strip the mag down, apply a small amount of silicone grease tp the seals, heat them lightly with a heat gun and reassemble the mag.
I would not advocate the use of maintenance gas inbetween games, its a total waste of money and you are more likely to do damage venting the gas each time you change over. (Freezing rubber is never a good idea)
As for the adaptor, always go with a genuine madbull one, they are available on ebay and work flawlessly. The cheap clones are pretty hit and miss.
Various Airsoft gas - fills
Yellow bottle Mapp - fills
Blue propane - jizzes everywhere