Nothing is perfect! Not even when it's brand new and unused and still in the crate. Most imperfections are within "allowable limits" and often not noticed, but they are there, nonetheless.
My 150K has been completely disassembled and inspected. There is normal surface corrosion "frost" within the wings and tail that does not affect structural integrity at all, and likely never will. I have found no affective means of removing all of this frost without reskinning the wings (an extreme overkill). There was minor filiform corrosion on the skins under the paint that easily polished out. The original galvanized steel firewall was strong, safe, and serviceable, but surface corrosion prevented restoration to my standards, so I replaced it with a new from Cessna stainless steel firewall. Removal of the old firewall exposed the only serious corrosion I've found on this bird. One of the extruded aluminum formers that attaches the firewall was exfoliated under an engine mount, and had to be replaced before the new firewall was installed. This could not have been found on the most extensive annual inspection without x-ray vision, but still did not render the airplane unsafe. I also found numerous rivet buck heads (decidedly original from the factory) that did not meet accepted standards so they were drilled out and replaced. Some of them were truly ugly, but again, were not unsafe! I also found factory routing of electrical bundles and fuel lines left much to be desired, and some minor rerouting and rebending was needed to prevent chafing and to avoid sharp edges on structure. Some aftermarket avionics wiring needed rerouting and clamping to provide proper clearance from flight controls (evidence of chafing was already apparent - this could have been dangerous). The wings and tail surfaces were out of rig as were all flight control surfaces, and cable tensions were almost non-existant on the flaps and ailerons (although you couldn't tell by flying her, except for a minor tendency to drop the left wing hand's off). To do what I'm doing on this bird would be extremely cost prohibitive if I had to pay someone else to do it. Most of this would never be part of a normal annual inspection, let alone a pre-buy.
