I have one of these on the 240D and the Excursion, not on the 300SDL yet:
http://www.fumotousa.com/
The oil drains a bit slower than removing the plug
, but it avoids damaging threads
. Nice feature on these is the way the valve locks into place when closed. You can even install a clip so the valve will not rotate at all while in use, but I do not see that it is necessary based on design.
(ref. previous thread:
http://www.peachparts.com/shopforum/showthread.php?p=2376270#post2376270)