Leaking lids on any master usually mean the rubber seal under the lid is not sealing well against the reservoir rails of the master, and in my experience it's because:
1) the master body reservoir rails are not flat,
2) the master body reservoir rails have nicks in them,
3) the bail (wire clamp) is not adjusted to hold down the lid tightly enough against the rails,
4) any or all of the above.
Due to casting tolerances being poor and due to rough handling, the master cylinder bodies are very often not flat, or have damage, right out of the box, especially rebuilds.
A local grey beard rebuilder here puts his on a belt sander to true them up. I don't have a belt sander (yet), so I true mine up on the bench (DON'T do this on the the car) - I put wadded up damp paper towels in the reservoirs to catch the filings, and use a flat file to clean them up, then I repeatedly vacuum/wash/bench flush the unit to ensure no errant filings are introduced into the cylinder.
20 + years, no leaks, no damage.