steering pump

MY PUMP NEEDS REPLACING, 2001 E320CDI, AND ITS ONLY WORTH A SECOND HAND PUMP, I RESEARCHED THE PART NUMBER AND GOT 2! 0024667101 AND 002467401 THE DESCRIPTION OF EACH SAYS IT FITS MY MODEL BUT WHY WOULD THEY MAKE 2 PUMPS? I TAKE IT THERE IS A DIFFRENCE? ANY HELP APPRECIATED.