I had the same problem. Horn not working and indicators not self cancelling.
After removing the steering wheel I found that the central two pronged collet, that engages with the steering wheel and drives the horn contact slipring and indicator cancellation, had worn down its prongs. this had caused the horn wires to stop rotating and they had been snapped by the motion of the steering wheel.
the ideal solution would be to replace the collet and horn wires but I managed to repair both, not sure how long they will last.
andy
September 2010