Thanks for all the info given. Let me clarify a few things since the questions have come up.
I have been RV'ing since 2007 in a (then new) travel trailer that had a ext warranty so I do understand my systems and diagnosing them but all repairs were done by dealer.
I briefly owned a Class A gasser that was older (1999) but I only had to do one minor repair myself while I owned it but had no problems taking it on the road. I was lucky enough to find one that was well maintained by previous owner (boat racer) who just bought a loaded newer Class A diesel pusher. I caught up with him a few weeks after I bought it because he left some racing equipment that I returned and heard him detail all the huge repair bills he had to perform on his "newer" purchase that is one of the reasons I am asking myself.
I work part time in an automotive business that repairs/rebuilds cars and trucks and have found that accessing service manuals, finding quality shops and performing preventing maintenance minimizes catastrophes but I like to hear feedback from other owners and the internet helps bring that to help me avoid common issues/problems.
My current house was 40+ years old when I moved in but it was "newer" to me because the house I moved from had newspapers from 1912 removed from window sills (stuffing) when I replaced the original windows so I am no stranger to older things lol or remodeling.
Some brought up a good point that I hadn't considered about full timing vs part timing on use of RV systems. Up to now I was just worried about the aspects of the chassis. The original owners used it part time for about 2 years then full timed in it about 10 years but he was methodical on proper use and maintenance on the systems. They have aged beyond the point where they can comfortably manipulate everything to use it so it has been sitting for a few years but they do test it regularly and taken it out a few times. That actually is my worst fear how the systems will operate after sitting for awhile. I want to be clear I do not want to rebuild an older MH because I know the truck systems can become expensive (used to drive trucks). But replacing or updating appliances would not be a deter me from a good deal. As far as I can tell everything works now but of course that has to be verified.