A bit late due to holidays but:
Do not forget to mention the possibility of a loosening clutch centre nut!
These tend to come loose sometimes leading to difficulty in changeing gears.
Did Timothy sort out his gearbox?
I only ask because my change was getting progressively worse. I had bleak thoughts. It turned out to be a loose nut on the rocker shaft in the doll's head. Now the change is very good.
