I'm working on my brother in laws ML500, when I went to do an oil change the 13mm plug is overtorgued. I'm looking for advice on how to loosen it without breaking it off, I have a replacement one, but don't want to damage the pan. Any help would be appreciated.

Use a 3/8 breaker bar or slide a pipe over your ratchet wrench to make it longer.

New crush washer is mandatory.

Clean the area around the drain plug and then apply some heat.