Is there any reason not to make the drain as Bruce did? Looks like a simple and useful mod . A conventional drain plug also seems a good solution. Either method should make changing that bit of oil less of a mess.
When I did the recent primary work on the Rapide, the old oil that drained out was almost as clean as the new oil that went back in.
I can't remember when it was last changed. It's got to be 15 thousand miles ago or more. Thankfully, the primary compartment on the bike doesn't ever lose or gain oil. That's likely why it stays clean.
If it is clean in appearance, I can't see much reason to change it.
Even with this level of maintenance abandonment the primary chain looks as new at 35,000 miles.
If there is a functioning mainseal fitted, I would expect the primary oil to stay as clean as the gearbox oil does. That seems to be the case on this bike.
Without the seal and with engine oil pumping into the primary, the primary oil would tend to get both dirty and over full in a hurry.
Glen