This thread shows something neat about Sturmey Archer, and Brit designed mechanicals in general:
Built well to last a long time. No seals to wear out, just suitable tolerances.
Just about any oil will do, because it won't be resident that long. Add new oil regularly.
Early Brit motorcycle engines used this same strategy, it was called "total loss oiling".

I had a '59 Triumph TR-3, the main rear seal was a "labrynth seal" a system of grooves and lands that threw oil off and was drained back to the crank case. British cars and bikes were known to mark their spot, but so many survive today, the designs were effective.