So the message here is new caravans are a lottery (and they shouldn't be) three to 5 year olds are usually ok, but beyond 5 years or so it again becomes a lottery, and an expensive one to repair those that fail.
You don't have to get cars or commercial van panel seams resealed at 5 years so why are caravan manufacturers' so far behind the reliability curve?
The new(ish) caravan construction techniques may have improved the survivability of leaks, but it seems it hasn't stopped the leaks occurring, so in reality the manufacturers have not made any real progress in about 100 years of experience of making better sealed products!
And despite decades of experience with front and rear mouldings failing they still continue to use them obviously incorrectly designed or manufactured.
In my opinion it should be perfectly possible to design and design the manufacturing of a caravan that survives fault free for at least 6 years, but the manufacturers have seen the gullible end-users coming and do as little as possible to get product out of the factory regardless of its fit or finish.
The problem is the buying public are too eager to get their hands on new caravans and they accept them in substandard condition, which simply encourages the manufacturers to skimp on design and product testing.