Measure the valves -- if they are undersized, get undersized guides if you want to keep them. Usually, on MB engines, you are best off to just replace with standard guides. The valve stems normally don't wear much.
Do take a look at the valves themselves, though. If they will be near the wear limit when ground, get new ones, they aren't that expensive.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!