I have a MIM fretless with a rosewood fingerboard which is in great shape after being played regularly for years. I only use flats on it and for the last 2 years I've been using chromes. The fingerboard beneath the strings is a bit grubby. Is it best to just clean this with nothing more than a damp cloth and then wipe dry? The only other treatment I use is an occasional spray and polish with furniture polish which I find works well to nourish the wood.