Just drained the differential fluid in my 560SL and found something interesting. The fill plug has a washer, but the drain plug does not. That seems kind of strange. Looks like this was the first time mine had been removed and the WIS seems to confirm the set up, so I think it's right. Just curious why. Seems like the drain plug is the one that ought to have the sealing washer.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles