I don't entirely agree. I have spent plenty of time being frustrated because of the shutting down of websites that once freely distributed material. When we are talking about "old manuals and inserts" etc, I don't see that any particular secondary source site has much claim on them at all, and I think it far better that the data/information be spread around. If I reference a work in a paper, I reference the actual author, not the library where I found it. Of course the situation is different when we are talking about original material (e.g. "unique procedures and hacks, custom photos" + any actual commentary text or analysis).

In the past I have also frequently mailed site owners indicating errors - and I cannot recall a single instance of a response. So I no longer bother.