The class has been working fine, if it ain't broke don't fix it.
agree with you Chris, but Fly parts are very hard to come by and expensive. Maybe we could restrict it to a certain part - Slot It SIKK04 is replacement axle kit with spur (36t), alloys wheels, axle, bearings and grub screws for Fly cars. I put this in my M1 and it works a treat.
This would not be a requirement as such, purely an option if needed
You wont get just the spur gear from Fly, you have to buy the whole rear end but that will still be cheaper than the Slot It SIKK04. If it came down to it any Fly rear end will do if you only need to replace the gear, it just needs to be the same width or wider so it can be shortened to the right width. Try Ged he has lots of stuff hidden away, MR should have something even if it isn't the exact rear end, if they don't then Pendle UK have them.
If it is just a case of spur gear problems then maybe just the Slot It SIGS02 - 36 TOOTH 19mm and keep everything else standard.