I've actually found the "E Class Owner's Bible" book to be pretty helpful with basic maintenance stuff like the trans fluid/filter change. Basic torque figures and easy to follow photos. There is also some useful stuff at - News.
The last couple filters I've installed had a cork gasket stuck on each hole, and the old gaskets came back out with the old filters. Maybe the old gasket will turn up in your drain pan.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)