Here is another twist for you. Let's twist again.

If a track, or indeed a complete album, has been downloaded from the internet in what way does this differ from buying used LPs/CDs from a market stall? To avoid being totally unethical let's say that said album has long been out of production and can't be obtained from any of the usual retailers.

For me tracking down the legitimate owners of obscure tracks such as OP describes goes into the too hard basket. I think that the best we can do is to not in any way assist in copying and passing on current or recent recordings, and pay for what we want ourselves whenever that option exists.

I enjoy my music collection, and I feel that it may be of value to others in the future because much of it is obscure.

There are blogs which have a number of old LPs digitised and uploaded. On one of these there is a post from the original artist thanking the blog owner as this artist no longer had his original album and couldn't obtain it anywhere. So yes, that can be a valid point.