I've just purchased this loco from Rails Of Sheffield, it takes a 21 pin decoder, can I use any decoder, been looking at one from Hattons, that looks a good price.

This loco on a circular track one of the wheels usually jumps the track, it can be any of the wheels, I also have a set of points that it derails every time it passes over, I have three other Bachmann and three Hornby locos, that pass over these points with no problems, thinking of sending it to Bachmann to see if it can be fixed,
I am a club member and a couple of experienced members have looked at the points and said they are okay.
Any ideas what could be causing this loco being a serial derailer?