Phalcon51,
I just finished rebuilding my 90 300 SE, a 722.351.
Some pointers:
- NO special tools needed.
- Leave TV cable (Pass side on trans) connected to trans during drop, first disconnect from top.
- Drivers side elec connection is a bit tricky - see manual to remove by rotating collar then pulling.
-Cleanliness is key. YOu will see what I mean if you open the throttle body and see a small strainer - the screen must be a 1/10 mm grid - a speck of dirt would clog this. I covered a 4' x 8' plywood with sheet plastic and used every bit of space.
- Power wash before disassembly if possible.
- I used a 6 point thin wall deep oxygen sensor socket (1 3/16) to remove the large rear nut. I filed the additional 6 points in with a metal file - worked like a charm. Use a small sharp pick to open the depressed divot, then unscrew.
- I used the same manual you have - it is not intuitive and it took a couple of reads - also things becme clear during disassembly.
- Disassemble and take digital pics, also group your parts (eg B1 piston assembly) there are hundreds of parts in this trans!
-Your throttle body, front pump, and tc should be OK unless you find metal in your pan. Flush the tc with kerosene. Check throttle body for ease of movement. Take action if sticking or loose.
- Replace front and rear seals - use a puller if none available drill 3 holes then screw in sheet metal screws and pry out.
-Replace all frictions and check the steels for burning - replace if burned or damaged.
-Check all clearances per the manual. You will need calipers to do this - the special tool noted in the manual is a spacer which makes measurement easier by providing a straight parallel surface.
- DO NOT disassemble the planetary section unless you feel or see something amiss - leave in one piece if possible.
- DO replace all lip seals in both clutch packs. You will need to drill out the rivets to replace lip seals.
-PAY SPECIAL ATTENTION to the teflon split seals on the main shaft - I pinched one which resulted in no 4th gear and had to pull trans 2nd time to fix.
- I paid less than $300 US for the Master rebuild kit + both bands. This is less than one way shipping for a rebuilt trans. I got my kit from AXIOM distributors. They also sell tc and all other parts.
- You should pay attention to shift pressure after the rebuild, especially if you have a diesel.
- MB Doc and David Poole are very knowledgeable if you get into a pinch.

Other than the effort, it was an adventure diving into this beautiful work of engineering, especially the ravengaux planetary gear sets!
Let us know how it turns out - maybe a Do-It-Yourself article.