Jord, they'll never last as long as OEM struts.. mine have done 20,000km with no problems, and I'm sure there are plenty of others in the same boat. I've sold a set of replacement dampers to one guy who did 60,000km on HSD's before they wore out.

Ivan Tan and Denver use them in their race WRX, 4 years and counting.

That being said, a set of OEM struts lowered on super lows won't last much longer than 50-70,000km before they wear out (they start getting "crashy" over bumps).