lisimac,looking at my manual which is for a 928d could your coupling hub be out of alignment to where it's throwing your belts off?also it says the spring coils should be extened to a length of 3" by adjusting the idler adjustment J-bolts.you should have two adjustable J bolts and one spring attached to them.if these are too tight might explain why your pullies are failing as they aren't greasable.also might explain the one broken spring.hope this helps,let us know. russ