Help please: Audi 100 2.2 EE (1989) auto trans

I have just taken ownership of this 'ole beauty (in my eyes at least) for a very very reasonable sum. The previous owner had filled it with gas and as
he left the servo the trans refused to shift up from 1st. He was able to limp it to his home where it sat for 3 weeks and i bought it, full tank of gas and a faulty trans.
I'm a car nut and love projects. I've always admired the Audi but they were way out of my $ range until this example.
The previous owner seemed to take care of the visual side of things but it appears totally neglected the maintenance side of things when it came to mechanics.
Today i drained and removed the trans oil pan and kept things as clean as possible. The trans fluid was dark brown, probably mixed with diff oil (failed seals?).... but in the bottom of the pan i found a part that looks very important. There were no other surprises, just thick black goopie trans fluid.
I have only the Haynes manual to go by which doesn't say much on the auto trans so can anyone tell me what the part is and where it came from! What i need is an exploded diagram of the machine..... the Audi manual i guess.
Is there a filler plug for the diff section? Haynes talks of one being leftside just rearward of the driveshaft flange. For the life of me i can't see anything that would be a filler plug. There's a large flat steel disc held by 2 bolts above the left driveshaft that's all. Anyone able to help?
Here's a link to a pic of the part i found in the oil pan...
http://www.clubphoto.com/_cgi-bin/app.pl/albums/large_image_view?id 97482& link_code=sa01_17
Any help truly appreciated, and sorry to have made this a bit of an essay.
Pete (happy with his 1st Audi he wants to save from going to the crusher).
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Nice car. Mine: '91 100 Quattro 5spd.
Pete wrote:

All it needs is a little TLC

A common issue with the Automatics is for the trans and diff to 'exchange spit' due to the seal which separates the two fluids. The way you describe the trans fluid it sounds like this is the case. Usual fix is to drain and re fill as you have done. The issue is that they do not have a trans oil level dip stick however that is available if you talk to your dealer about it. Might take some talking but they are a real part that sells for about $25. Some people just drain and measure the oil that came out and then replace with the same amount.

The audi manual wouldn't help much either. I have never BTDT on the Auto so recommend that you go to AudiWorld and search the threads history or ask the question. I remember others talking about the same experience with a part in the pan. http://forums.audiworld.com/v8 /
Also seem to remember that getting the pan to seal again can be an issue. Don't tighten too much.

Again I haven't do this but several discussions on the AudiWorld forum. I think that the drain is a 17 mm allen. Others have said that before you drain it be sure that you can get the filler loose because they can be the biggest problem.
Changing the diff fluid is a good idea but the trans oil that has located into the diff is not nearly as big an issue as the diff in the trans.

Hive her a little TLC and you should be very happy with the results.
Tony
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I had trouble finding the diff filler plug too but it is there! It is very close to the driveshaft, quite low down. You'll need a 17mm hex driver from memory. I eventually found it when I had to replace the CV boot. When I took off the driveshaft I suddenly spotted it! Took the opportunity to check the oil level while it was off as it looks tricky otherwise. (This is on a 3 speed auto btw).
Gary
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