Ok, now that's I've read thru all of this thread, I'm ready to give my 2 cents.
I'm one of those people who are very wary about buying from a private party just because you don't know what you are getting. While you still don't know what you are getting from a dealer either, at least they have gone thru the inspection process on their dime and you are getting a feeling for that dealer. When you need to bring the unit in to be serviced, you already have a relationship from them and since you bought from them, I believe they treat you better. Sad thing these days but it's true. I'm sure these people took excellent care of their rig but you just never know. With a dealer you can buy an extended warranty or a warranty of some sort to cover the MAJOR things that could give you problems, you can't do that with a private party.
A year ago we bought a used 2002 3295RK and bought the warranty for $2,000 with it. It was the best money we ever spent because about a month and a 1/2 ago our furnace went out and it was over $1200 to fix it. So we have paid for more than 1/2 of it and still have 3 years left. To me the "insurance" or "piece of mind" is priceless.
Just something to think about. Remember, everything has their problems, but the fact that the manufacturer is willing to stand behind their product makes me feel so much better. Even if it takes a couple times to get it right, at least I know they are going and willing to try.
Ultimately, obviously the decision is yours. Since I'm sure you are going to be spending a great deal of money on this investment, the decision might be a difficult one. Good luck and what ever you decide to do will be the right one for you and your family. We love our Montana and would and probably will buy another one when they figure out where to put the washer and dryer in the 3650RK.