Couple of Qs...1)Any comments on performance/duability of Suplex coil springs please?

2)Can anyone direct me to online details on procedure for fitting rear road springs to Smart Roadster Coupe `04/`05 plate please?Usually don`t bother with manuals but reckon it might save time on this one.She`s sitting down on the drivers side rear,can`t see anything underneath so suspect top of coil is broken.It`s done 40,000miles,hasn`t been thrashed,I`m only allowed in the passenger seat ;) but you feel every pothole&manhole cover........so does the suspension I would guess.First became suspicious when the driver appeared to do an odd correction mid-corner at times,usually her driving isn`t too alarming.Now I understand car was oversteering on right-handers and understeering on lefthanders.