So I just changed the oil in my wife's 2000 e320 wagon and noticed what appears to be leakage from the passenger side of the front differential. I am assuming it's from the axle seal. I could not find a single post from anyone with the same problem. So i have several questions:

Where is the fill point to check the fluid level? I didn't see it, but I didn't spend too much time under the car as it was 15 degrees outside. I guess the fluid level should be up to the bottom of the fill hole, right?

What type of fluid does it take? All my local benz dealer would tell me was that the factory stuff is $27/quart and it takes 2+ quarts. They sure aren't very helpful to DIYers there. Wouldn't even tell me the spec. My local imported parts place sells Schaeffer fully synthetic for ~$10/quart, and it apparently exceeds the spec. Anyone ever used Schaeffer stuff? Is the diff fluid just hypoid gear oil? Would Mobil 1 gear oil be adequate?

Last question: how bad is the axle seal replacement procedure? Don't really want to do that this winter, especially given the ridiculously low temps and all the snow that refuses to melt here in Colorado.

As always, thanks much for the advice!

Here are some pics:

Does it have a vent at the top like the rear diff? They often leak a little.

__________________
Prost!

If the vent is in fact the source of the leak, then don't worry. You have enough oil. Remove the drain/fill plug and let drain any excess.

__________________

Don't Chrome them; polish them