I use a leather seal on my sloper, having remade that bronze bush to be a snug free-running fit. But I agree with you.. yours will probably run perfectly fine as is, even with that thread on the quill. (At least the spiral tends to push the oil back in to the bush eh!)
I attach a photo of the bsa assembly drawing which shows the seal.
with the original felt seal that i removed from the engine when I rebuilt it, or my leather seal, I found the seal snags on the timing gear nut and so spins with the crank and polishes the concave bush, rather than becoming shredded. After around 1500 miles the oil pressure on my tank-mounted gauge drops from 3 to 1 PSI as the seal eases off. But after 4000 miles i had good compression but rebuilt with a high compression piston & barrel and new seal on the crank anyway. All was still otherwise good at 4000 miles including the bore and the new Alpha big end.
I know the oil gets to the bore from that blue haze that the handbook describes. I have my oil knob open just 3 flats (1/2 turn from fully shut). It took me quite a while to find the confidence to turn it that low... But I have undertaken regular long motorway journeys with full camping gear like this (e.g 2014 John Bull, BSAOC Summercamp in Belgium etc).
I think the only downside maybe something I experienced when first running in with the knob open 3-5 turns, i.e the timing side will tend to fill more than it need do, So oil can get past the cam followers and even fill the push rod tubes (I sealed my telescopic push rod tubes with leather seals only to have the oil then rise to the rocker box!).. If you don't have a felt seal in the taper behind the Magneto timing gear, it might exit also between Timing chest and Mag... However... just closing down the oil supply solved all that.
I use Morris Golden Film SAE 40 mostly. It revs more freely than SAE50 but using SAE50 on the 400 mile summercamp trip I only used 1.5 litres of oil. These bikes original pistons have no Oil ring of course, and there is no engine breathing, so I was quite pleased at that.