I always wondered where the little shavings of aluminium were coming from when I changed the oil !

After putting some of the bits together, I have one complete tooth and just the upper 2 prongs of the second tooth

One Primary Driven gear assembly and 7 new friction plates later, it runs again.

We flushed the engine out with petrol first, then by hand with a set of long grabbers and finally with some clean oil. The bits on the petrol can above are what we removed. There is still another large chunk in there somewhere, unless it has come out as shavings.