The school where I help out recently completed the full SID's for their C 172's. One had the entire vertical fin replaced after so much internal corrosion was found that it was not economically repairable. I know of another Cessna SEP, not ours, where the SID inspection found a cracked wing strut attach casting, failure of that and the wing falls off
The SID inspections are probably about 30 % overkill but almost all C 172's are over 35 yrs old and many are pushing 50 years, so a it is reasonable to expect some expensive surprises in almost every example......