Then I suppose you already have a cartridge gun, although partially worn out. My suggestion: buy a used swiss Wanner gun, plenty on eBay. The wanner is small, one hand operation, stiff maneuoverable nozzle. Easy to bring in the car if you wish. Excellent quality, will most likely outlive you. But not for cartridge! So what I do is using an old cartidge gun, filling up the reservoir of the Wanner from the bottom and you are good to go. No mess, no spill, could do it in a white tux. Once the Wanner is filled you can grease the front suspension several times before you need to fill it again.
2004 V6 Roadster