Just checked an original inner cover. The spiral groove is cut much closer than the bush pictured, at least 3 turns from the oil hole to the outer edge.
The spiral runs anti clockwise in the same direction the shaft turns, just like a big "Left Hand Thread" The bush pictured above has the spiral running the other way and is NOT CORRECT for the inner cover but is fine for the crankcase end of the idler shaft.
Marvic. The small cork washer under the large domed dynamo drive gear is more of a simple way to eliminate end float on the shaft, rather than a true oilseal....that's what the spiral scroll does. Under normal circumstances a small amount of oil weep into the compartment would be expected, happily mixing with the grease lubricating the standard chain drive.
If there is next to no float on the shaft you can assume the washer is in place. To inspect the bush the inner timing cover and dynamo drive gear have to be removed. The gear has a taper to fit the shaft and will pull straight off, using a two legged puller.
For now I would clean away the oil, reassemble and review again after a few miles running. The timing gears are marked with dots and dashes to ensure correct positioning on assembly as in normal automotive practice. Plenty of hints here on the Forum achieving an oil leak free dynamo mounting, and as mentioned this very problem was recently discussed and simply solved.
Swarfy.