Don't worry about it, Marvel Mystery Oil says on back of their bottle for auto transmissions and gasoline engines. Transmission fluid has better EP additives (Extreme Pressure) than engine oil. It will help more than harm.
A lot of trans builders put a quart of "engine oil" in trans to help lube and and clean the valve body .
A lot of trans builders put a quart of "engine oil" in trans to help lube and and clean the valve body .
