What year MH models are too old to consider buying?

Water leaks will probably be the biggest, most expensive problem. Rubber hoses can be replaced fairly easy. Delamination is probably the biggest killer of MHs. Water gets into the sidewalls and dissolves the glue holding it together. That can also be caused by excess heat but it is usually more expensive to repair than a MH is worth. Get one that does not have laminated walls but hung walls like Newmar, some Monacos, and other more expensive coaches to avoid that problem.