I have a CAT 3126E now and have had 3 Cummins engines as well. One current Cummins. I would not make the decision to buy an RV on whether it has a CAT or Cummins engine. They are both bullet proof if you do the maintenance religiously. You can get a dog in anything mechanical. I have also had a Mercedes diesel and was not fond of it but it was ok, not b great. Get the serial number of the CAT engine and call the CAT RV line, 1 877 777 3126, and ask them for any history they have on the engine. The techs on the hotline are super and very helpful.