Here's a different electrical question.

On my computer desk I have a table-top power distribution box that lets me
plug all the computer stuff into one central place.

While it has some claim as a surge suppressor, since I am in Florida where
lightning storms are the usual event during the summer, my method of
protection is to disconnect the distribution box from its a.c. outlet. (The
cable modem uses a quick connect on the cable line coming into it.)

The problem arises because the wall receptacle that is being used is
inconveniently behind the very heavy desk. To make things easier, I cut the
power cord to the distribution box at desk-top level and rejoin the ends
using an in-line plug and socket so that it is easy to disconnect from the
line. The connectors I used are a good quality pair made by Hubbell.

The problem: It has become increasingly difficult to mate or open these
connectors. They have been in this use for more than five years.

The male ends do not show any signs of distortion.

Is there an appropriate lubricant?

I could just buy another set of connectors, but a lube job would be a lot
simpler. Is this a big box item? If I have to go to a real electrical supply
house, it is cheaper and quicker to replace the set. At $3 a gallon
travelling very far for a small item doesn't make sense