As far as I know the yellow fluid is bad, Good guess is that it is original. When you checked the level, was the car running? If the car was not running the reading should be real high on the stick. If the car was running it should be between the lines on the high side. If it was me I would change the fluid and filter then run a few hundred miles and change it all again. Reason being it sounds that this fluid is in real bad shape, you want to get it all out and all the sluge and metal filings. Good luck

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Stable:
1973 450sl
1978 red diamond ice vette
1975 steel blue convertable vette
2002 steel blue dakota quad.