Considering purchasing a 2003 Monaco Diplomat 40 PWD

That's a lot of coach for the money. I'm no expert but in doing some research a while ago I seem to remember people suggesting an oil analysis to check the health of the engine.

Of course, there are the expensive things you know about - tires, batteries, interior/exterior, etc. The main thing to me if I were looking at that coach would be to get as much inspection and information about the things you can't see right away - Mainly, the engine. But also the tranny and other drivetrain components.