Don't know if you want to try what I do, but it works . I sanded the master on a flat surface , I thought I did a good job but low and behold it still leaked out the front of the master , so what I do now is take the top off clean the rubber gasket with brake clean then clean the top of the master after you have it all nice and clean I take some automotive silicone and put a fine film on top when you have a fine film all the way around , replace the top. Works for me. With all these aftermarket tops hard to find a good one.