I grew up on Japanese bikes. Starting on a honda qa-50 in kindergarten. To my last which was a suzuki gsxr-750 in my late 40's. Never had or rode a bmw. But if they are like Japanese models, then check all gaskets for signs of leaks or gasket replacement. Especially in hard to see places. Hondas in the 80's and 90's head and valve cover gaskets were notoriously leaky. Well if you rode hard, they were. And i would run the piss out of them. Just look for signs of baked oil stains on the motor. The bike pictured looks like it needs rode hard. . So i would ask to see behind the plastic !!!
I quit ridding due to fuckin crazy ass drivers in cars. My daughter's boyfriend has a Hayabusa he said I can ride. Maybe at a race track. But not on the street.