Co worker has an air powered Lincoln, it is unusual in that instead of one shot per trigger pull, it fires continuously while the trigger is held down, just like the .45 caliber version

. It works great and flawlessly.
As far as grease guns leaking, that is something you cannot avoid, the liquids and the solids tend to separate in the grease, especially under the pressure of the spring loaded follower. I keep mine in an old kitty litter tub on a bottom shelf. It can leak all it wants. I have to wrap it in rags when I pick it up to keep it from dripping all over the floor. The grease lasts longer and separates less if you pull the follower rod back and lock it back when not in use, takes the spring pressure off the grease. If you need to bleed it, release the spring follower to put pressure on the grease then, loosen the tube a turn or so and allow the air to bleed thru the threads, pump till it starts moving grease and tighten up the tube, works for me every time.
Charles