that is surface corrosion usually due to moisture. although the corrosion is not a major concern you should replace the reg *** it will not get any better. The main problem is that it will flake and get into the reg causing other issues.
do not clean it with any chemicals as this could lead to a bad situation the next time you fill it.
the bad part is you cant stop it but check more often and wipe it clean more often.
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