I thought I had bought this:
But when I played it it was this:
mystery track 1969 (UPDATE: now identified as Billy Butler & Infinity "Soulation" the B side of "That Aint Water That's Pollution" released on Mercury in 1970).
To look at, the 45 is Fountain FOA-1102 - the other side of the 45 is what it is supposed to be i.e. Infinity "Get On The Case", and the etched matrix numbers in the dead wax agree with the labels on both sides so there is no clue there.
It sounds like they are singing "soulation", but googling that doesn't help.
It's possible, I suppose, the group singing is Infinity although the style is somewhat different.
The mystery track is worth hearing but I just wish it had replaced "Get On The Case" instead of "Keep It To Yourself", which is a really nice track.
Can anybody identify this track? Please!
UPDATE: Thanks to Ana and Johnny (see comments) and Colin Dilnot via email for identifying this track for me. I also found another link (now mislaid!) that gave a bio of Billy Butler and stated that Stax were caught by surprise by the success of the Fountain release and couldn't press them quick enough. So in their haste to get some more pressed I guess they must have sent out the wrong master for the B side! I wonder how many more mispressed Fountain FOA-1102 45s are still out there?