Read about the sad true story of how the first owner was ruined by the US Govt because he was German immigrant businessman at the beginning of WW2, just like many Japanese Americans were. He was the BMW importer in New York, and managed to finagle one of these seventeen R51RS racers from the factory.
In truth, BMW sold very few motorcycles in the US in the 1920s and 30s, as protectionist trade policies introduced in the mid-20s levied a huge tax (up to 100%) on 'heavy' imported goods. Thus BMWs were rare and very expensive in the US
The 'RS' was a pushrod 500cc ohv flat-twin
Emil Recke's troubles began when AMA track officials ignored the bike making the fastest qulaifying lap at a race in Langhorne Pennsylvania, and when the US finally entered the War in Dec. 1941, Recke, as a German national and 'enemy alien', had his bank accounts seized by the US government.
Suddenly broke, he was forced to sell his BMW dealership, parts stock, tooling, and motorcycles to survive, for which he was paid pennies on the dollar given the ramping-up of the propaganda machine against anything, and anyone, German (or Japanese). After selling nearly everything he owned, all he had left in the world was his most precious possession, the R51RS which had been entrusted to him by the BMW factory. When it became clear that this, too, must be sold, he did what he had to, and sold the bike. He then took his own life.