I recently bought a 1985 300TD as well. I just wanted to ask some clarifying questions about things mentioned in this thread:
Note: I edit this as I get more answers.
coolant: Zerex G-05 50/50 with water
transmission fluid and filter: Apparently any Dextron ATF will do. Takes around 6.75 quarts, but check after 5 quarts. Whatever filter fits also will do, may need to special order it.
power steering fluid and filter: Same fluid as for the transmission. Doesn't take much, check the dip stick. Going to use a siphoning technique, or get a pump of some kind.
rear differential fluid change: 85W-90 or fully synthetic 75W-90 works. Takes 1 quart and less than 1 cup. The pump-and-hose method used on dieselgiant's site (
here) looks good. Probably find one at a Petsmart or the top of a soap bottle.
brake fluid: DOT 4. Found it!
air filter: Replaced this today. Simplest thing ever. The 3 rubber mounts under the filter housing are soft and look amazingly perfect for such a old machine. Need to replace the clamp that connects to the top of the engine valve cover.
The more I work on this, the easier it's getting! The rotor looks a little messed up. There's a lip on the edge, which suggests that the brake pads are eating away at the rotor. I'm not sure if I should go ahead and replace the rotors, or get a different kind of brake pad and replace all of them, or both.