I always rub a bit of ACF 50 over the unused bottom part of the stanchion (or the top bit under the bottom yoke for RWU forks).
If you need them refinished, Brookes Suspension offer a rechroming service for £165 per pair.
https://www.brooksuspension.co.uk/mo...nchion-repair/
They also do DLC and Ti-Nitride coating, which I considered when I had my forks worked on by K-tech, but the money ran out.
Maybe at the next rebuild!
If the spots are outside the stroke of the sliders and merely cosmetic, can you remove them with some Scotchbrite, polish up with Autosol and then protect with ACF 50?