W126 series with gas V-8s are known to experience cam wear with high mileage if oil changes were not conducted on schedule. These engines also require valve jobs around 200K to eliminate oil leaking into cylinders around the valve stems. Third, if the engine still has a single cam-drive chain, you need to replace it with a double chain and new guides. With 288K, you may want to think about having your engine rebuilt from the ground up, which will also include new bearings, rings, etc.