Coilover Sleeves

You are right, I just didn't think that a worn shock can cause a significant change in ride height. That would be an interesting experiment though if we could see a shock-spring combo vs just a spring compressed under the same weight

Springs should be long lasting, true, but usage / weather / make can make a huge difference imo. For example I've never seen or heard of a broken T16 spring, but I saw broken springs from other brands, that were MUCH younger. And I heard some of the Celica owners here that their springs got somewhat lower and lost "power". Just think about a spring constantly rusting. It's outer "skin" comes down in layers one after the other, the whole spring loses diameter with every layer, and that alone is enough to make it weaker.