lift the car, remove the lower cover, the bolt will be facing the left wheel ( well it does on my c220, donno about yours).
if u get an oil filter, it comes with the washer, especially if u're buying it from oriely (wix brand). 8-9 bucks.
u can get a oil filter cap tool from autozone. u know where the oil filter cap is right?
the drain plug bolt is a # 13. while leanring from my mistakes, learned to tighten it just till it stops moving. no yanking!
oh and as for plugs, i change mine every 30k miles just to keep the fuel and preformance at a good level.
i go with Bosch plat plus 4. but hopefully some c230K owner will verify if you could use the same.
good luck