Good morning all,
What should I look for when buying a second hand gearbox?
It may be out and drained already but if not or still in vehicle, remove the drain bung and look at the oil. It would be nice if was clear and see through with a golden honey color. This would indicate it was replaced regularly... or just before you got there.
It it has a metal flake or sparkly shine... that's probably what it is. White milky oil has water in it possibly from being submerged. I have drained what looked like silver paint once and another time it was more like dirty plain yogurt.
Inspect the bung.... it has a magnet on it. A black 'paste' is normal. If clean then someone recently cleaned it. If you find this.... walk away.
It's part of a bearing cage. I have pulled a bung with several ball bearings clinging to it.