Mine lasted 10 years & 50000miles. When they started to sag, they lost an inch of ride height in a 12 month period. Main thing was how their tension had dissipated. A lot more banging from the back end. Replaced with 4 leaf GME springs.
www.gmesprings.co.uk Also the front springs had to be changed for similar reasons.
(Oh just to add. I also had Antitramps & panhard fitted. The antitramps help protect the springs & stop them flexing in the wrong place. )
