1937 clam shells were the only vertically split covers Indian used, all across the range. May have been 36 as well ? Maybe the owner has sport scout or standard scout cylinders fitted from this era?
The later chief covers are available with a small O ring at the bottom.
The amount of oil leaking from any of the covers can best be described as a light weep if the bike is oiling correctly, and is barely noticeable. If the breather set up is working, and the rings are good,, this weep is negligible. If there is an issue with the breathing, excess crankcase pressure will force oil up the tappet guide blocks, past the pushrods, and there will be an excess accumulation inside the covers, which will leak copiously.
I will reference John Bivens, of Indian Engineering here, and use his advice. A well set up standard factory Indian vent system works absolutely fine if everything else is set up right, so there is no need to attempt to improve on it on a stock bike. The only caveat I would add to this is that this applies to the post 1929 system. The early 101 and CG/CGP short frame motors with the breather on the left side of the engine have a tendency to continuously vent oil, hence the factory update referenced in the May (?) 1929 Service Shot. After this date, the factory moved the breather to the timing cover adjacent to the magneto, and the Service Shot gives details on how to retro fit this system to earlier bikes.
