I installed a set of KYB's on a W115 and after less than 3 years parted the car out. On inspection, the shocks were found to be leaking, the rears particularly. I threw them out even though they were still functional. As for performance, I liked them! They were a bit more bouncy than the new Bilsteins I recently put on the "new" model 220/8. As someone once wrote, KYB = Keep You Bouncing. I think they are not that bad, a little more spirited than Bilsteins, which for a diesel might not be of importance.
Bilsteins have the edge for lifetime, and are my recommendation.
I knew someone that had a Boge fail, complete loss of fluid only a couple of years after purchase. That kinda thing can happen to any parts but leaves me thinking their Quality must be marginal.
Dieseldiehard
1971 220 (gas) 4-spd manual 104041 or is it 204041?
1979 300TD w/ ’85 turbo engine 288975
1983 300D 237300
1985 300TD 205437