the only time i have seen or heard of damage to ABS systems is when people are prying, banging, or smacking the rotors off, and do damage to the abs sensors on top of the axle or the ring around the hub . what damage does pushing in the piston do to abs???
It isn’t the pressure that’s the problem. I’ve read of contamination forced back into the lines by the caliper pistons interfering with the operation of the valves in the hydraulic control unit.
Push them back in if you like. It’s a free world. But jeeze Willey, try to be nice. Insults are entirely unnecessary. And useless.
Their concern is dirt contaminates getting in the ABS modulator by pushing the old fluid backwards in the system. If you flush your brakes every 2 years like you should, there IS no dirt to contaminate anything. I think that’s over analyzing a simple job.