Breakdancing Drum!?

We have a Hotpoint Aquarius 1200 (WM 64) - today, it began making a terrific banging sound on spin and tried to breakdance across the kitchen floor!
Taking the lid off showed one of the suspension springs broken, but nothing else apparent. Running the machine showed the drum to be leaping around like a mad thing, even with the spring replaced. If switched onto one of the spin cycles, it runs up to high speed, then slows, speeds up again, slows and repeats the process.
Are there any other suspension supports or springs apart from those at the top, or should I be looking for another cause? (Worn motor brushes have been suggested, but I don't know if that would cause this problem)