I'm in the process right now of doing the valve guides,valve seals, chain rails, headgasket, fuel injector seals/o rings, oil pan gasket.
Engatwork, is pretty close on the dollar amount (if sent out to a shop). My brother and I , are doing all the work ourselves, so all I have to pay for are the parts (I was charged $364- to have the guides put in and to purchase them. I already had the seals). While I was at it I also changed the fan and clutch as there was too much play in the fan.
It's funny but I too am going to have to have my tranny done as there are leak from the tranny also (the Benz has approx. 205k on her). Make sure you go to a tranny shop that's familiar with Mercedes though. I brought mine to a shop I thought to be pretty damn good about 2 years ago and I'm still kicking myself to this day. It was definitely a poor choice. $600- later and the car is still leaking. When finished with the motor she's going to a shop that's familiar with Mercedes. Good luck and let us know how you make out.