Not exactly an answer to your question but I did read somewhere that the engine in our C400GT is Piaggio. Does anyone know for a fact if this is right?
I've read a fair number of posts in a few forums in which folks think the 400-series engine is from the Taiwan company Kymco. I can see how some folks might confuse that, because Kymco was involved, for some years and models, with BMW's 600/650 scooters. See
https://en.wikipedia.org/wiki/BMW_C600_Sport_and_C650GT
But attributing the 400 engine to Piaggio is a new one to me ... and does NOT appear to be the case. According to this web page -- which looks to be on an official BMW site -- the C 400 scooters are produced by a Chinese company called Loncin:
www.bmwgroup-werke.com
The C 400 engine may, of course, be similar to any number of engines made by any number of companies -- there are only so many ways to produce engines that have reasonable life, power, etc., and conform to emission regulations -- but appears to be made by that company in China.