I own a pair of Millennium Plus 5's and both have maple fingerboards....pretty much plain maple with black dots. One of them I bought from GC and it is in excellent condition but the fingerboard was soiled. Some players have acidic hands or just eat fried chicken and don't wash their hands before they play and the fingerboard gets soiled. Here is before:
It looked about like that up until about the 12th fret.
I had read that folks use calcium carbonate to help pull oil out of gunstocks so I acquired some and gave that a try but it did nothing except waste a little time and money. I won't go into details since it didn't work.
I dug around on the internet and found a post on the Ernie Ball Musicman forum about a guy who tried this and that and then finally tried a paste made out of Barkeeper's Friend (a cleanser that is at many grocery stores). Barkeeper's Friend has oxalic acid in it so handle with care. Anyway the guy said he left it on the fingerboard for 2 minutes and the before/after photos showed the fingerboard looking good when he was done.
I removed the neck from the Millennium. I removed the tuners from the headstock and taped over the face of the headstock which has a clear gloss finish. I mixed up some Barkeeper's Friend into a paste and applied it to a couple of fret areas and left it for 2 minutes and then wiped and then rinsed it off. I dried the neck but first used a solution of baking soda to neutralize any residual acid.
It seemed to help a little but not much. So I applied the paste to all the soiled areas on the fingerboard and left it on for 5 minutes. After that I wiped, rinsed, applied baking soda and rinsed again. I dried the neck with a towel and then use a hair dryer to completely dry it. I was pleased to see it looked a lot better. Probably 8 minutes would have removed all the stain, however, I was satisfied with the result I got with 5 minutes.
I took the neck outside and rubbed the neck, fingerboard and frets with 0000 steel wool. The wood and the frets polished up nicely. I used compressed air to blow off any steel wool fibers that remained. I got excited and reassembled the bass prior to taking an "after" photo but here is one with the strings installed:
As you can see, it looks fine now.
I will now work on the second Millennium 5. It was set aside while I worked on this one. This one has TI flats on it and plays/sounds amazing. I will put rounds on the second one so I can have one with rounds and one with flats.
I am a happy boy!