Nice one, Simon. That must have been Hurricane Models, same place where I got mine.
I've got some of the parts you need (pm to follow)
You can get replacement bearings from RCbearings.co.uk
http://www.rcbearings.co.uk/index.ph...roducts_id=289
You need twelve of these for the axles and rear gearbox. Rubber sealed are better for the damp. The front ones are rarer. You could try to rescue them by soaking overnight in lighter fluid or brake cleaner.
If you've still got your old charger you could just get some new(ish) Ni-mh cells e.g.
http://cgi.ebay.co.uk/Racing-Battery...item3f07c342f6
These and your modified might be enough for the kids.
No doubt other members will have some helpful suggestions for you too.
Good luck!