I always had that problem with my conventional grease guns and kept them in 5 gallon pails, too. With the Milwaukees, I don't see the leakage - I have them hanging from the girts of my shop. LockNLube has rubber caps for the coupler that prevent spillage. They also make a barrel cap that helps a bit. I still had a mess with those, though, and they do harden/crack after about a year or two and need to be replaced. I'm only using the coupler caps with the Milwaukees and no mess through two Texas summers now.
Same have a locknlube on my Milwaukee and it hasn't leaked.
