Whats the best stuff to use when doing a change? Should i go with something synthetic? How often should it be done in my 87 300SDL, and how much should i buy to prep or this job, I'm estimating about two quarts, will i need more?

Thanks

75w90 synthetic. It will take a little more than 1 bottle.

I believe my 84 126 is 1.1 or 1.2 quarts to fill. I don't have my FSM on me but I believe yours is 1.2 quarts. So yes, 2 quarts is what you need.

I use Mobil 1 Synthetic 75w-90. As always it is up to personal preference if you use synthetic or not.

I also remember hearing that if you switch to M1 syn, you should do another change 1 year later because it really cleans things out.

One note- When you do the change make sure you remove the upper bolt first, then the bottom one. You don't want to drain it and have no way to fill it.

Have fun!

__________________
2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

I just did mine this weekend. I HIGHLY recommend getting a pump and hose for the bottle...I only had the pump, and it was quite the contortion act. I am known to do things illogically, though..
Not sure how the SDL is set up, but even with the long, pointed tip bottle, I wasn't able to reach the filler hole because my exhaust was in the way.

__________________
Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

I had a pump when I changed my 126 but I'm pretty sure I got one of the two bottles up there and dumped oil in without a pump. But I would get one just to be safe.

Here is a nice write up courtesty of dieselgiant- http://www.dieselgiant.com/mercedesreardifferentialfluid.htm

__________________
2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

The W-126 doesn't require a hose or a pump. The clearance is sufficient for the pointed tip on the Mobil-1 bottle. The exhaust is on the opposite side.

Nice. I was a little surprised that my drain and fill plugs were on opposite sides of each other. Oh well. I've got some time before I have to deal with that again. No blow torch needed either!

__________________
Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

What diff fluid would be recommended for the locking diff in my 300D?

__________________
93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

LSD? See here:
http://www.peachparts.com/shopforum/showthread.php?p=2041592