you can buy just one ?!

 

Barring any failures of the coilovers like leaks (blown seals etc.) or broken parts, I guess the two possibilities are springs that are fatigued and either "settle" or change the spring rate, or that the dampers are no longer controlling the spring action properly. I am close to 45k on my CS now, and I don't notice any problems with them yet. There might be some change in the specs, but I can't feel it.
At some point, I will probably either have the dampers rebuilt or just replace the CS and try something different. Might be good to talk to a tech guy at Tein to see what they recommend...

 

Mine has a lifetime warranty. No worries

 

This is great about bilstein pss you have

 

I currently have around 75k on my Tein CS coilovers....mainly highway miles though; however, I do drive aggressively. So far, no signs of oil leaking or ride degradation.

 

yeah i would say 50-60k miles easy for a tein coilover

 

haha good, so when i sell my tein cs later say with 50k miles i could still say it's like new?

 

I don't see why Teins would wear that much if you're mainly doing highway miles. I'll bet I get 75-100K before I have to rebuild.