I have one of the rigs you describe.
CC roofs are fiberglass caps. Therefore the most likely leaks are through-the-roof penetrations.
I have had a leak at my roof AC and at the Sat Antenna cable entrance. The leaks became apparent when the ceiling grew a stain of water and dust.
The remedy was to seal the entrance and shampoo the ceiling. The first leak was about 8 years ago.
Wall or window leaks have not been noticed. The molding that encompasses the roof cap and sidewall joints has sealant, that should be replaced occasionally. I have not resealed the windows during the past 14 years.
Any coach can develop a leak.
I suspect, a Country Coach from the 1990's is less likely to have a undiscovered water leak as long as you stick with a non-slide rig.