The 10.9 designation are the proper "case hardened" bolts to be used. All too often you'll find someone has replaced them with the 8.8 "standard" (non hardened) bolts. If they dont state "10.9" on the head of the bolt then they shouldn't be trusted. ANY and I mean ANY time you find a loose steering gear box bolt on any Benz/car, remove the existing bolts and replace with NEW! Never re-use a hardened bolt! It's not only YOUR life but I just might be on the same road as you.