Not only was the machine trying to drive the knackered gearbox but of course the blade disc is always connected to the engine so a 21 or Osprey needs to be in good order for trouble free starting. Another problem that afflicted 21s was that the throw of the standard throttle control was not quite enough to move the carb lever to both full choke and stop. One or the other but not both, especially when there was a bit of wear in the linkage.
As far as your purchase goes, how was the machine described? If for "spares or repairs" it is definitely "buyer beware". If described as "used" the implication should be "may be worn but at least working" .If the ad mentions a drive problem - again you are in trouble.
New transmissions, or even repair parts, have not been available for many years, so you are at the mercy of sellers' honesty.
Some years ago I wanted a 15" petrol Flymo to meet a customer's particular requirement and purchase one that was described as "just serviced" . It plainly hadn't been and I supplied both ebay and the seller with several images to show that it hadn't been . Ebay did nothing and the seller eventually offered a full refund providing that I payed all the return carriage costs and then put me on a "blocked buyer" list.
