Master Cylinder - Cover Leaks

If I need to buy a new cover and gasket to fit better I have seen so many ones for sale on ebay that end up being a bit smaller than the one I have, or the 2 bumps on the top are reversed. I need the one with the straight front and the curved part on the rear. I have read also the Ford makes the same type but it still is not the correct size, and I hate to buy the whole cylinder just to get the right cap. I have measure the cap and none seem to be the correct size.