I have used silicone grease, but WD40 is more-readily available. It also
wets better, and creeps into the hidden nooks and crannies. I give
everything a good dowsing before and after assembly,

At one time I thought silicone grease would save wear on N connectors until
I used the spray on wattmeter slugs and found it completely insulated the
shell contact. I since found it caused an SWR hump on N connectors even if
it were just a spot on the threads.