Newbie to TC needs help with Mi3.5

[mattf77]

Hi there,
I have just bought an Mi3.5 to have a go at touring car. it seems as though the diffs are completely jammed and there are a few parts that look like they need replacing.

diffs- if you turn one wheel, its opposite wheel should turn in the opposite direction, yes? these don't twist one wheel and all four turn.

spares- are these available or do I need to use parts that are compatible with other models, which models are compatible?

how do I know the dp of the spur gear to get the correct pinion?

thanks

Matt