Very interesting!
AFAIK, the Hercules bikes were about the only air-cooled Wankels made. It wouldn't be easy keeping those working well I'd guess. Thermal control is the reason that Suzuki went liquid cooling but in the days before CNC machine tools, it wasn't easy to control the machining of the combustion chamber shapes. Apparently, it nearly sank Suzuki at the time.
I had a good chat with a former Mazda R&D guy some years back after their difficulties with the RX8 sports car (they had a to replace a large number of engines that were fairly new but wore out to the point where they didn't run). He told me that the problem was that some of the engines seemed to last forever with virtually no wear at all while in others, the rotor tip "apex" seals would wear out within a few thousand miles. They did endless testing and metallurgical examination work but never really figured out why this was happening. The problem, aside from the cost to Mazda, was that once they gave the customer a new engine, the car was no longer "numbers matching" and the collectors didn't want them so the resale values dropped fast and the reputation of the car was weak. Too bad - it was a cool car IMO.
Along with the manufacturing and durability issues, the fundamental problem with the Wankel is poor thermodynamics: the volumetric efficiency is not that high and so fuel consumption is poor and also, they had to inject tiny amounts of oil into the combustion chamber to lubricate the apex seals and that oil was burned along with the air-fuel mixture, and consequently, exhaust emissions were also quite high. This meant that they needed big catalytic converters (i.e. lots of platinum so $$$$) and it brought down Mazda's CAFE (corporate average fuel economy) ratings.
Too bad, because the Wankels run very smoothly and produce lots of power on small displacements.