Would humidity be the reaon?
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Could it be changed bearing tolerances due to dissimilar metals ? My rega has a brass bearing housing, with a steel shaft: these metals expand and contract differently. It's pretty common to have a brass or bronze housing with a steel shaft, and a steel, ceramic, or saphire bearing ... all different materials.
One of the Brinkmann turntables has a small heater in the bearing housing to maintain a constant temperature. It seems a bit extreme to me, but perhaps there is a measurable difference in performance.
While factors like those mentioned above are probably all contributing (including the beer!), your speculation about temperature + Chadnliz's speculation about humidity are probably the biggest factors, at least IME.
The suspension in a cartridge is made from an elastomer. Elastomers are more sensitive to temp/humidity changes than other solid materials. When temps and/or humidity rise, most elastomers soften. With less resistance from the suspension, the cantilever can be deflected more easily and reach greater excursions from a given force (ie, groove modulation). Result: faster transient responses and greater dynamic range from the same LP.
Every cartridge I've used (dozens) has required more VTF and antiskating in the winter (cold and dry) and less in the summer (hot and damp). Depending on the climate and the cartridge, the VTF differential can be .30g or even more.
Experiment a little as the year goes 'round. You'll learn more about optimizing your rig and hear more music at all times, which might even satisfy Pbb. ;-)