[JSeery]

I wouldn't think the aluminum top and/or gasket would be the issue. It is a lot more likely that the top of the master cylinder would be where the problem would be. The master cylinder is not designed to have a seal with the fluid level all the way to the top and also under some pressure. It is going to have to have a good sealing surface on the master cylinder and then enough clamping pressure on the cover to get a good seal.