Bingofuel,
This was quite a serious problem, the FAA issued AD 2008-03-10 to address poor quality design and build, some aircraft had to have a complete belly skin repair, and this on aircraft less than 2 years old.
Quote,
SUMMARY:
We are adopting a new airworthiness directive (AD) for certain Cessna Aircraft
Company (Cessna) Models 525, 525A, and 525B airplanes. This AD requires you to inspect the lower wing skin structure, forward wing spar, lower fuselage skin, fairings, and the external fairing frames for corrosion; repair any damage found; apply a corrosion inhibitive sealant to the fuselage
fairings before reinstalling; and disable the cockpit mounted pilot relief tube. This AD results from leaking of the cockpit mounted pilot relief tube, which caused corrosion of the airplane structure. We are issuing this AD to detect and correct any damage from corrosion of the airplane structure.
Corrosion of the airplane structure could cause structural degradation and lead to structural failure of the airplane with consequent loss of control.