There are a few issues.Hopefully something is obvious to you as it isnt to me 😕
That flywheel does not appear to belong to that engine, it is an early flywheel without the O ring seal in the flywheel, (this type relied on a paper gasket instead). It has been drilled for 8 dowels, but your crank only has the standard 4 dowels, and the flywheel was never sealed to the end of the crankshaft properly anyway. There is also a wear groove where it contacts the lip of the oil seal, this means it may not be tight enough in the seal and will leak. The oil seal isn't fitted correctly, not deep enough in the case, and not even straight. The end of the crank, the case, and the main bearing all look slightly "battered", as does the flywheel, all these can contribute to leakage.
As mentioned by GARRICK.CLARK, the pool of oil behind the oil seal indicates that the oil return channel/drilling in the crankcase may be blocked or at least restricted.
There should be 3 shims behind the oil seal, did you remove them for the photos ?
Are you sure it is a 1958 30 BHP engine ? it looks later than that, (only the flywheel is the early type). What's the engine Number prefix code ?