And the average across all 2-3 year old cars is 5%.

It does not tall us much unless we would also get some information on how expensive it is to fix the problem.

A 5% problem rate can be worse than a 15% rate if the cars in the 5% category have issues that are more than 3x more expensive to fix.

They fail TÜV. You fail TÜV if you polish your headlight glass, or mount replacement panel/bumper/hitch without special certificate.