at some point, business is business. if you were the first owner and these were six months old, that's one thing. you are the third hand owner (at least) and these are several years old. they were probably out of warranty when you bought them; certainly out of warranty now. if i buy a six year old car from a second owner and the motor blows because of a design defect, the company has NO obligation to fix it. whether they SHOULD fix it is another matter......
IMO, $400 is cheap as hell to get four shocks overhauled. if they install their new style shim stacks and seals, you basically get an upgrade from their old sh1tty shocks to their newer ones. probably you'd get a warranty, too.
i can tell you that even if you'd spent $7,500 on a set of 4-way motons, you'd still be rebuilding them now.
Ahh but car manufacturers do honor warranties and recalls/campaigns no matter the number of owners. I am not asking k-sport to replace them for free but knowing there was a distinct problem with the design of their shock a good business would give the customer a break.