Originally Posted by elp_jc
I'm pretty sure you just stick a 3/8" ratchet extension in there, like most cars. If not, it's going to be a 14 or 17mm socket; nothing even the cheapest tool set doesn't have.
Just remember to fill it with the car flat. I don't even have to lift the car, but you might have to lift it to break plugs loose and for the final tightening, as you won't have much leverage with your arms extended under there. When it's time to do it, I'll fill it with a hose extension over the rear right tire; much easier than lifting the whole car (without a lift, that is). Good luck.
I don't think a 3/8" ratchet extension would work. It needs a 6 sided tool to R&R the drain and fill plugs. E36 differentials used a 14mm hex tool.
Does the E9* M3 use the same size?