5000 hrs. is not a lot of hours if it has been maintained properly! I have buddies in the trucking industry that have many, many more hours than that on theirs and still running great!
Is there a rule of thumb on longevity? Mine has a little over 10,000 hours. Power tech tells me they can last 10,000 to 80,000 if properly maintained. They suggested I change the generator end-shaft bearing. I have no maintenance history, however I do know that my rig was owned by people in the construction industry and presumably were knowledgeable about maintenance. I also think anyone who runs a generator that much must have maintained it well but I can't be sure.