Spoke to my dealer after buying a used 2017 Thruxton R and brought in for the required inspection after I changed out all the fluid’s, replaced the oil filter, lubed the cables, cleaned, lubed and adjusted the chain and checked tire pressure. Typically Thruxton’s seem to lose some tire pressure when they sit over the winter. He pointed out the oil weeping just above the oil level site glass. Since it was there, I told him to replace the o-rings. $8 in parts might be a little steep for a couple of o-rings but there was no labor cost.
He said “they all leak within 2,000 miles” and it’s a minor fix. Not sure if it is on the earlier models 2016-17 or if the factory has corrected the problem by now. Anyway, I park my bikes in my garage on a 12’x15’ rug I found put out for trash and have never seen any oil staining the rug so it obviously doesn’t leak that much.