Here's my experience:
Took the old 280SE for the "full-service" right before a family trip from California to Oregon. Loaded up the family, luggage and off we went. Everything seemed fine, except when we stopped at Kalamuth Falls Oregon for the night, I kept saying hmmm it certainly smells a lot like differential oil around here (sulfurous smell). My wife said :Of course it does, there are logging trucks all over the place". Satisfied with that we spend the night and continued on.
At a relief stop the next day out in the middle of nowhere, I then noticed the differential lube all over the back bumper!
I limped into the first little town, drove up to a gas station, put in on a lift and yep! No fill plug in the differential. The mechanic and I tried to find a plug, but nothing would even come close.
Finally, after re-filling with diff oil, we used a short piece of garden hose, an old lug bolt, and get this: bailing wire to hold it together until we could get to Bend where a MBZ dealer is.
When I tried to pay the mechanic and he said: "Oh yeah sure. You take it to the fancy Mercedes dealership with bailing wire all around the differential and they'll laugh you out of the place. No charge buddy". I slipped a couple of twenties under his phone when he wasn't looking.
Long story short: I return to the infamous fast change oil place with the bill for the new plug and the oil, and they said: "oh sir that is impossible". I wrote the headquarters, presented them the bill and they paid it. They also sent along several Free Oil change coupons. I DON'T THINK SO!
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)