Not original, but available
Originality is often seen as the highest good among BMW motorcyclists.
There is a lot to be said for that. Certainly when it comes to BMWs with a heavy historical background; for example, the Duite WWII sidecars.
Those exotics are now all worth the grand prize and the parts supply is ... Well: just fine. Even the original tires from WWII are available again. The 'getting' from that must be available or taken with an enormous amount of salt.
The part prices are in line with those of the complete engines, And those engines are usually very museum-like and they are hardly allowed to play outside.
Because do you imagine something breaks? CASH DESK!
A possible rescue, or help comes from an unexpected source. Until a few years ago, brand new CJ 750s were made in China. These are the direct genetic descendants of the famous BMW R71s.
A lot of the parts of that machine that are still new and inexpensive to obtain are completely identical in terms of dimensions and tolerances with the BMW 'Originalteile' of yore.
The importer of the side-valve Chinese, MOTORWERK.nl, has been sitting at the table with the various clubs that are busy keeping the WWII happening.
And together they become increasingly enthusiastic. Their very practical approach is that motorbikes are made for driving. And if that is affordable, then that is absolutely fine.
Below the margin the idea is: make the engine usable with good parts. Although they did not come from the German factories. But keep all original parts. Even if they are broken.
Because a well-running spanning Span with many Chinese parts is worth less than a non-running BMW full of broken Originalteile.