Well, odometer stands at 15600 miles. So, long time no fuss.
The hose is still in good shape and no kink; the way it runs it may well develop one when worn out.
The week prior to the 'incident' the air filter got a routine check and was found clean.
Still a valid theory and an incentive to give tender care, as in thorough cleaning, like on a dirtbike -getting behind every cover and corner-, even when you're tired, outtimed, and the garage floor is cold and hard. (Craig, I should know better but no HF around here).
After I had cleaned all traces, I ran the engine without airfilter and airbox open. All fine, no oil blowing. Likely, if the level had been a tat lower it wouldn't have occurred, I guess?
So, a freak event after a week of extensive riding, with lots of rain on dirty roads.
These observations may be of interest to keep in mind when people report 'leaks'. Mostly it is just excess lube kicked off by the chain behind the front sprocket. But those who find proper engine oil could benefit from the explanations here.
Made a composite picture.
Top row is the underside before and after cleaning. A large stain might have confused somebody it came from a drain plug.
Bottom row is the oil stained airfilter and the part of the gasket that sits on top of the breather chamber.
Thanks for all advice.
By the way, I think this labyrint is a cool idea. Beware of minotaurs though.