I would be wondering how you can inspect the unit until you get it clean enough to see what you are looking at.
In our industry, I DO know that no one knows it all, but I am so often reminded of the thought that "people who can not or will not do the job should refrain from telling those who are doing the job, how to do the job".

I also like the one about:
"Do you know who makes 'people who think they know it all' crazy?
People who do know it all.

Who makes both of those groups the -most- crazy?

People who can tell the difference.