My diesel has 240,000 miles and has just broke in, usually diesel engine that have been maintained properly will go 3 to 5 hundred thousand miles and if other parts around it begin to fail just replace those parts
I agree, I use Shell synthetic oil and have an Amsoil remote dual by-pass oil filter system, changing it at about 12,000 -14,000 miles. also consider Amsoil synthetic in the transmission if you tow a lot. take a samp le of your oil to Catapiller to analyze the condition of your engine. cost is about $14 and it will tell you a lot about the engines condition now.