I've got an '08 ML350 with 36K miles. The dealer has recommended doing the transfer case fluid service ($65) around 40K miles and then says that the differential service ($110 total for front and rear) needs to be done at 60K miles.

These are all very small amounts but I hate wasting money on things that aren't needed. The manual does not call for those services at all. So, I called MB's corporate office and was told that unless there's fluid loss, MBUSA does not require doing these services at all.

Can any of you think of any compelling reason to ever do them?

They're leaking or they've been under water.

You mean you'd do the service if they are leaking? Why? Why not just have them add fluid if there's a leak, which is already part of Service A and B.

If they were leaking I'd have the leak fixed. This would be a warranty fix if age/miles are right.

Transmission, Transfer case, differential require service at 39K miles. I had then done for $700 ish before I traded it in for '11.

I plan on keeping mine for a while, so I plan on dif service at 100K miles.
You better do the transmission at 40K with the new spec fluid or else.

The manual clearly states that transmission service is required at 39K miles. There's no argument about that. It says nothing about transfer case and differential service and, as I posted above, Mercedes-Benz corporate has confirmed to me that these services are not required at all.

Where are you seeing that transfer case and differential require to be serviced at 39K miles?