Transmission Problems - Please Help!

[MB300se65]

I’ve got an 88 300TE wagon that began having transmission problems a couple years ago and instead to fixing it I parked it where it’s sat ever since. I recently bought a used transmission from Pete Toro here in the forums to replace it, which I’m going to do this weekend, but I’m curious what could have been the problem with the original one.

It’s been a while since it went out and if I remember correctly it all of a sudden shifted into neutral on me while driving down the freeway. I pulled over put it in park turned off the engine, restarted it put it in drive and it drove fine for a bit and then dropped down into 1st or 2nd gear. I repeated the process of pulling over and restarting it till I got home.

I checked the oil level which was fine and a nice clear reddish color. However every time I drove it over the next few days it was constantly shifting up and down through the gears and into neutral while I was driving. It was shortly after this I parked it for good and noticed about a week later all the transmission fluid drained out of it onto the ground.

I’m definitely planning on replacing it with the used one I just bought, but I'd like to know if someone can tell me what may have transpired with the original one that would make it act like this. I’ve got a 95 E320 wagon as well and if I’m not mistaken I believe they both use the same transmission, so if it’s not too major I may R&R it and keep it as a spare.

Thanks

MB300se65