I gather you are talking about the Brake Master Cylinder. I got a new gasket which fixed the problem of it leaking. Also having to much brake fluid in the reservoir will cause it to leak as well. Failing that you can change over the whole brake assembly for another brand, cost a hell of a lot more than a new rubber gasket. You will have to do the change on the clutch assembly as well.

The Master Cylinder Cover screws are not done up to tight as well. if they are done to tightly the gaskets gets deformed and allows the brake fluid to seep out.

If you reservoir paint is being eaten away because of the brake fluid there is nothing you can do about it. Get another cylinder of Ebay or put on an after market control sets.