The valves on this car require the removal of the camshafts and replacement of some precision ground shims to adjust the lash or gap. It takes a while and yo need new parts (gasket for the valve cover, and the shims), so look to over $200 unless you do it yourself. Not that big a deal as the stuff was made to come apart and go back together nicely. I learned to do it myself, and now so does my son who drives the car. It is an overnight thing as I measure the gaps, take out the hardware, measure the shims and calculate what I need. Then you have to buy them, and I am lucky as the dealer has a "set" of these that they have relatively little use for, so they usually have what you need. I do that the next day and reassemble. If they order the part the car sits for a few days. You will have this happen at the dealer or at an independent, unless they stock the shims in sets.
If the car does not roll well, you should have your brakes checked first. You may find they are grabbing a little, which is a sign you need to have the calipers rebuilt. Grabbing brakes heats the hub up a lot, which is not good for the grease. So, you might need to grease the wheel bearings, but if they are so bad as to affect the rolling of the car, they likely need to be replaced too. Bearings usually make a noise, like a growling, especially when you turn, before they get grabby.
Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)