Using proprietary parts is NO excuse for poor parts back-up and customer service, especially for a certain large company building folding bikes in Taiwan. The only time I had to order a part from that company was when the bolt holding the frame clamp safety catch (on my first MU SL) fell out on the way to work.
I managed to find a similar bolt in my home workshop to use and then I ordered a replacement.... 18 months later and there is still no sign of that bolt turning up at the dealers... not to worry the bike is long gone and I upgraded to a Brompton...

Talking of which, Brompton probably use more proprietary parts than any other folding bike company yet every single part is readily available and in stock at several dealers / online sites. So as I say, there is no excuse for such poor service.