Ginger
No probs.
Given that the lubricant originally used on the Vickers and Lewis guns froze at altitude, I wondered if the mount didn't incorporate something like ball-bearings, that way a spot or two of rust wouldn't have mattered too much. Of course, if the thing was made of aluminium, rust wouldn't have been a problem anyway.
As Bluebottle said "Just a thought"

Graeme