Hobie makes a curved disk that works very well and are dirt cheap. they can be tricky to get in the right spot and stay in place during stepping.

I used to use the gatoraid caps but they really don't last more than 2 or 3 uses. the white teflon disks last dozens of times (i usually lose them before they wear out).

I am sure grease helps, but i can't see it working as well as a physical barrier between 2 metal parts that are under a lot of pressure, but then again... Mike has a g-cat, was a seabee, and knows his shiznits...