Ansmann Master Smacker replace/upgrade.

[themagicnumber]

Hey,

I picked up an old Ansmann 'Master Smacker' for a couple of quid knowing parts were going to be difficult to get.. and it clearly needed some..long story short - parts are like rocking horse wotsit and the spur gear (Ansmann calls it a middle gear) is knackered.
I can only find one seller of a legit part, he only has one, so for future reference does anyone know of an interchangeable part from another vehicle (it's a 64t to a 22t pinion).

I plan to replace the current electronics as it's all seen better days..would I need to change the gearing from the stock 64/22 to accommodate a 10t brushless?