I had them on my Z for 3 years. After 3 years of constant driving since I drive it as a DD they finally started to leak and eventually blew (the fronts only). We got ahold of the manufacturer (Ksport official) and they would NOT send me replacement parts or even just 2 new fronts. They were major dicks about it and wanted me to buy an entire new kit, even though my rears will still perfect. I had to take them off and now I'm back on stock springs until I get new springs, and yes, I will never buy from them again! I'm going to go with the ARK GT-F springs, they give it a major drop and a smoother ride. Plus, I don't have to worry about replacing $1300 dollar coils when I could just pay $388-480 on springs - which look just as aggressive.
