What's the best/safest cleaner to use on the push button auxiliaries on the Heritage 3000? I've got some over on the far side of the console that are tough if not impossible to push. We rarely use more than the first 4 as this is a FOH console, but I would like to keep everything working properly. The one's that are tough to push still work fine, I bought this console used and may have just overlooked this to this point.