It can go a long time between changes and there are different schools of thought... 30,000 - 100,000 miles (U.S.) are the extremes, 50,000 - 60,000 miles (U.S.) is probably a good target to shoot for.

P.S. alwawy remove fill plug before removing drain plug...

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14