Change Differential Fluid Highly Recommended
I just finished changing the differential fluid on a 1989 420 SEL with 218,000 KM (135,000 miles). The old fluid was dark olive green grey colour and it smelled aweful. I highly recommend changing the rear differential oil especially on the older W126 cars. I used a synthetic 75w90, about 1.45 litres.
1989 420 SEL