I had to fill oil while riding in the Alps, not when I got back home. The oil level had dropped to approx 3,5 litres, so I topped it up. The 1/3 litre may not be important in comparison to the total oil capacity, but may be important enough to prevent starvation of the oil pumps and thus engine parts. If BMW says not to let the oil level slip under the lower level of the looking glass, that's reason enough for me.

- Boxers do consume oil, sometimes more than 1l per 10000km/6000miles, so your not checking is hazardous, but that's your priviledge.

- Topping up is required when oil level is dangerously low in any bike or car.
- The carter of the R12 boxer engine is divided into front/rear compartments. In a car, the inside of the carter has fins to make sure the oil is kept in place during hard cornering.
- In any bikes' or cars' manual it's advised to check the oil level regularly. All cars I have owned up till now consumed oil. My current car does not, but as engines wear oil consumption goes up and so I continue to check it regularly. And, last but not least : a sudden dramatic increase of oil consumption is a sign that something's wrong, and I'd want to know.