Peeling decals was a common problem thru the years around that model year. Many, including myself and my 2007 Montana, have replaced the decals. That may well be why others you saw look new. Mine do, .... now. Replacements were available from Keystone up until a couple years ago. When I removed the decals the areas under those were very shiny compared to surrounding areas. That may have made them look darker in pictures.
I have never had any water leaks around my shower. Only leak I have ever had was due to a failed black tank flush anti-siphon valve.
$19.7k is considerably below NADA "low retail". Would all depend on overall condition as to whether it is a good deal. I would look inside, outside, on top for roof condition and any signs of cracked caulking, under side especially at suspension, tires, check all appliances, check furnace and A/C(s), and any thing else you can see. If it all looks good, you could start with an offer somewhere below that and see how bad they want to sell.
