Gilly, drain plug gaskets...
 

In your opinion which is better? aluminum or copper.. I noticed MB techs use only copper drain plug washers.. is there a reason for this? I am currently using aluminum on my ML.. I also have access to plastic washers as well..

If the drain plug is removed to drain the oil (which normally isn't done, especially on an ML) then you would want to replace the seal ring. The seal ring used would be whatever MB calls for (MB part number) in a dealership, which is a copper seal ring.
If you have good results with an aluminum seal ring, I wouldn't question it, I don't think it makes much difference, but in either case I would replace it every time the plug is removed.

Gilly

I noticed..
 

on other cars the drain bolts threads are all the way to the end of the bolt head.. so basically you don't need a seal ring.. but I noticed the ML's M13 bolt has a 1 mm gap between the threads and the bolt head.. is their any reason why they designed the bolt like that? you need a new seal right definitely...

Little too much of an engineering factoid question for me. No idea why the drain plug looks different to you. Never seen a car yet that didn't require a seal ring of some type on the drain plug.

Gilly