what did the last guy put in this gearbox

Drained the gearbox on the 13 inch. It came out the color of coffee and it smelled like a fish market had a gearbox. I don't know if I should run diesel through it, kerosene, or just fill it with what the book says and pray. The book is a photocopy of a photocopy.

Don't run it on diesel. Flush with the same oil you're going to use, drain, fill. Fish smell is old way oil and water. If there's metal in the drain, that's a different thread. Is there metal.

Sludge, not chunks. A magnet picked up a little dust and nothing I'd call a tooth. Flushed twice. It smells like oil now, which is a low bar and I'll take it.