Good morning Mr. Fisherman,
I know what you are talking about because I have seen this before on some old 295 machines. I don't know of a specific cleaning solution or compound that you could use to clean knobs and take away the stickiness. It is hard as a moderator to recommend or to tell you to try something that may further damage the knobs. I will say we do offer replacement knobs and I can provide you a part number if you would like to go that route.
One fishermen that I know decided to cut off some small pieces of heat shrink to shrink around the knobs. That did take away the stickiness. He took the knobs off first and made sure that the heat shrink was not extending over the bottom or the top of the knob. Seemed to work pretty good.
I was also thinking maybe you could try some type of adhesive removal solution like Goo Gone . Again I don't know how this will affect the knobs, it could make them worse. So I want to say that as a Furuno employee we cannot recommend such actions.
Kind Regards,