Its a design fault search the threads on here they changed the design and cured this about a third of the way through production. Yea the rear discs are expensive but were special ones only fitting the 260 and R75 V8 with 880 odd cars a very small run with high production costs. Im on the original discs at 75,000 miles and have gone through a set of rear pads every 17,000 miles.
Phil