Brake fluid will strip the paint off the tank and the brake lever/throttle assembly if allowed to continue. If you have the round type master cylinders, those often seem to leak around the base of the plastic reservoir, that "sits" into the metal alloy base. If this is the case, there often isn't a good way to repair them and they usually get replaced outright. The rectangular ones (from 1981 -> later) can leak from the base where the plastic reservoir sits into the allow base as well, though leaks there are often due to
failure of a small rubber O ring, which can be replaced. Both styles can also leak from the end of the plunger(where the brake lever pushes in on the end of the piston).
Look carefully in these areas for signs of moisture. Sometimes a spritz of talcum powder helps to detect moist surfaces (and give your "baby" a fresh clean smell) !
There are rebuild kits available for approx ~$50 US (last I checked) for the rectangular ones - they come with several different diameters of piston, so you must get the one that matches what is on your bike. There is a number that is stamped into the metal housing, usually toward the front/lower side that will say something like "15" or "12" or "13", etc.. This is the size (Diameter) of the piston in millimeters and is the size of the rebuild kit you should get if you are going to try to rebuild/repair yours. Before attempting a rebuild, you should probably take yours apart and check the condition of the bore (inside where the piston does its work). If it is heavily corroded and not shiny/smooth you may be better off ordering a new M/C assembly for around $150, as the replacement parts will only last a little while in a corroded bore. You can't clean up that corrosion easily - scratching the surface in there with something like steel wool will cause further issues down the road..
Anyplace that the brake fluid has gotten onto you should clean with water and some sort of soap - any brake fluid residue will damage the paint over time if allowed to sit there.
