Something as simple as caliper piston rubber not set properly could cause that. My Gen3 had the caliper piston seizing problem and I had to clean and lube them every time i swapped out my winter tires. Otherwise i would have had to replace the brakes every 2 years.
I believe your referring to the caliber slide pins that equalizes the pressure between the inner and outer rotor assembly; NOT the caliper piston seals themselves that keeps brake fluid from squirting out.
I just push them back and forth every time I rotate tires. The grease gets a bit peanut-buttery in between (because the normal motion in use of the brakes is so small, a fraction of a millimeter). Pushing them back and forth wakes it right back up. If I ever do that and notice they move roughly or feel in need of cleaning and regreasing, then I'll take them out and do that. Never happened yet. There are several other parts of the caliper that can deteriorate and cause problems with brake releasing and drag and are often totally neglected in posts that mention only the relatively reliable pins. The fitting kits (the springy metal clips that fit in the caliper bracket channels where the 'ears' of the pads slide) are what I most commonly find needing attention when I inspect my brakes. The factory dry, Teflon-like coating wears away after a while, and later, they begin to show rust, and the pads won't slide in them smoothly. It isn't expensive to replace the fitting kits whenever needed.