If it runs well, doesn't leak, and doesn't smoke, just drive it and keep the oil full. If the guides were severely worn, you would see smoke out the tailpipes when you release the throttle and coast down from freeway speed. If the rings were really shot, you'd see a lot of smoke when the engine is under load, such as while accelerating hard. You might want to have someone follow you and watch for smoke. I would doubt, however, that a properly-maintained M-B with the mileage on it that you quote would have major engine wear. Good Luck!