1984 300D Transmission woes

My transmission has not been enjoying this hot weather here. Recently it started slipping out of 4th gear. Sometimes it goes to 3rd, sometime it goes completely out of gear. I checked the fluid level,
and added some fluid. I also added some Trans-X to it a couple days later. Still no luck. Checked the level again and realized I had overfilled it. I drained out enough to get it back to normal, and the fluid was a beautiful red color, no burnt smell, no dark fluid. I changed the fluid and filter about two years ago, and did a drain and fill (no filter change) about 6 months ago when I was diagnosing a "broken" throttle position cable. Turns out the cable was fine, but that piston was stuck. I worked it free and adjusted the cable and everything seemed to be working fine at that point. I thought it might be the B-2 piston, but the symptoms listed on this site don't match up with mine. http://dieselgiant.com/Mercedesb2pistonsealreplacementl.htm A few questions: What do each of the pistons control? (B-1 and B-2) I had assumed the B-2 because I thought it was for the 3rd-4th gears, but maybe not. Is there a set of springs or other pistons that could be the problem? Is it worth doing another filter and fluid change to see if that works without doing any other work?
Additionally, it was only doing this when the transmission heated up, but now it does it within 5 minutes of driving. I would prefer to do the work myself rather than a shop.
Thanks for any help and opinions.
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http://www.scribd.com/doc/24267811/Mercedes-722-3-722-4
What is the condition of the transmission you have now? Rebuilt (when)? Current mileage on transmission? etc.
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Wow, that is an awesome diagram. Thanks for sharing that.
I should now update to explain that I solved this with a little more research after I made this post.
The problem was the throttle position cable was too loose. It was not engaging except slightly at full throttle. When I adjusted it correctly, the problem disappeared and the transmission is shifting perfectly again. Nice firm shifts and hits the right shift points based on throttle position. Looking back, I realize that the upshifts were happening too early and I should have thought to check that cable sooner. Additionally, I now have the fluid at the correct level (it was overfilled previously). I did find out that my kickdown solenoid is bad though. It blows the fuse when I have the kickdown switched connected (behind the pedal). I just went back to my previous solution of disconnecting it and manually downshifting if I need to pass someone. Interestingly, this is fuse #14 that someone else is having a problem with. The A/C stops when this fuse blows.
To answer your questions: The transmission is performing excellently. I have no idea if it has ever been rebuilt, but whoever owned this car for the first 260k miles took great care of it. (I recently rebuilt the injectors and they weren't near as bad as I thought they would be.) Without knowing if I have a rebuilt transmission, I would assume the mileage matches the engine at 305k miles currently. Still running strong, and now the A/C even works. This is my daily driver for my commute into Atlanta every day. ~85 miles round trip.
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