If your S350 is an earlier model than 1996 (I think so because in 1996 MB offered the OM606 S300) then you have to replace the whole mirror assembly from a later W140. The mirror style changed and those housing covers will not fit the early style housing cover.

I'm only guessing about the door handle covers but I believe they are covers that either snap in place or have some adhesive.

Sixto
95 S420
87 300SDL