This listing is for a single door striker for W123 and W126 vehicles.  LEFT side.  Works for both front and rear doors, but most commonly the driver's door is the one that goes bad.  This is expensive, I agree, but the $30 URO/Meyle ones simply don't work right.  Mount this up, adjust as needed, and it will work well for 20 years.  Free and fast shipping from a Mercedes repair shop that's been working on these vehicles since 1985.  Thanks!