It doesn't look too bad a job to DIY , at least on my 500E. I'm figuring 1/2 day with my skills....or lack thereof.
Pretty sure all I need is the re-seal kit but at 142K...wouldn't hurt to put in a new one since I plan to keep the car a long, long time.
The cheapest price I can find new is about $550 for both pumps from a dealer....mind sharing where you found the cheaper prices? Or does your W124 not have the SLS? Bet that is where the difference is...