How do I properly clean oscilloscope BNC connectors?
Stick to the manual, which will likely tell you: No solvents, just mild detergent (i.e. a bit of dish soap and water). Use only if really necessary, and apply just a little using q-tips. If dry q-tips work, even better...

This is not really specific to RF connectors, just good guidance for any electronic device.

Inside the BNCs, pure alcohol might also work, but sometimes, alcohol will act aggressive towards rubber (and it will certainly do harm to some plastics on the front panel, let alone the markings). Also, alcohol will likely just spread out any dirt and leave it in the tiny spots once it dries. I tend to use alcohol only when I can wipe it before it evaporates, or as a last resort when detergent or purified water won't do the trick.

Back in the days of analog tapes and cassettes, alcohol was recommended for the tape heads and the capstan, but you were cautioned to not use it on any rubber (pinch roller!).