sox track1.flac fixed/track1.flac speed 0.985
I was going to recommend Playback Rate Shift here:http://www.foobar2000.org/components/view/foo_dsp_effectBut it only does whole integer %. Nonetheless, it's by the simplest solution and maybe it's good enough for you.
except for one. That one started out at +1.0%, then by the end of side 1 (GDR pressing...) it was at 1.2-ish %, and near the end of side 2 it was almost 1.4% fast when compared to a CD issue. Now speed on my trusty Technics, entry level as it may be, has been quite stable in my experience, certainly within +/- 0.1% from average. Since we are talking about an album with a slightly altered track list from the mid/late '70s that was edited on the Eastern side of the iron curtain, I am guessing that some tape machine had an issue that made it run slow, slowly coming up to proper speed as it was used.