From what I have heard replacing the timing chain alone is easy, but to do the rails you have to pull off alot of front end parts on the engine. If you put in a new chain and the rails are bad, the chain probably will not last long. maybe there is some way you can peer down in there and visually inspect the rails, ask an expert what to look for. If it were me and i planned to drive the car for a long time, pull parts off the front end, do the rails and any other parts that could be replaced while it is disassebled, like the water pump, belts etc while you can save on the labor charges. Also replace any cheap parts while you are in there, glow plugs, injectors, etc
2000 C230 Kompressor
1988 190e 2.3 - 225K miles, owned for 7 years. I cannot say enough good things about this car. Very well built, even at 225 it ran like new.