What specifically wasn't working? The only difference I'm aware of is
that you won't be able to distinguish between view/download for anything
other than Office documents, because that requires client-side
functionality that doesn't exist for other client viewers OOTB.

It seems completely inconsistent. I do see a record of a PDF that I
opened, but many (most) are not recorded.

Doing a simple test of opening a Word doc and a PDF, then looking at
the audit  report, I see the Word doc has incremented its view count,
while the PDF doesn't even show on the list.

Are you sure you aren't getting a cached version of the PDF (meaning
there is no server request for the file and therefore no audit  event)?

I wouldn't think so because PDFs that I freshly upload then try to
open are not showing on the list. I know the audit  view report is
getting updated though because I also opened a Word docuement and saw
its view count incremented.

How would I test & prevent this caching? It would seem like quite a
flaw in an auditing  solution.