Yeah and the RTR (Ready to Run) means it's put together .. HA!
It's put together, but only like any other mass-produced item, to a price not to a spec. You'd definitely be as well to re-build both diffs. It may be, I don't know 'cos I only ever had Team editions that need building from scratch, that the diff is simply locked by tightening it enough so it doesn't rotate, or has a dummy centre, you might be able to adjust it to work properly ..
Somewhere I have boxes of tyres and wheels and spares for these things .. I was club, and Area Touring Car champion a few years ago! Club champ for about 10 years .. just got old and my thumbs stopped doing what I told them to, that's when I went into refereeing ..