At Baltimore Brass, Dave Fedderly opened up the inside slide for me a little, and muscled the slide a little to stress it outwards for more friction. But it still is too loose. He told me to take off the outside slide and pull the sides away from each other more if is was still too loose, but that makes me nervous!

What I would rather do is find some real sticky, thick slide grease to use on that slide. Can anyone reccomend a good choice?
Also, I would try Vaseline, but someone once told me that is not good because it hardens and turns green or something. True?