Hi Joe,

You didn't mention what material the screws are made from. If your
using stainless switch if you can. Stainless socket head screws bugger
more easily than black alloy or plated screws.

I would suggest using a tiny dab of antisieze on the underside of the
countersink. We use an antiseize from Swagelock called high purity
goop. They make some impressive claims about this material and the best
part is you only need a minute amount.

Also you might look at going to Torx driver screws. These have a bit
more bearing area and don't cam out as easily as hex keys.
Good luck

Tom Lipton