After replacing hundreds of SMC’s on these bikes over the past several years, I’ve seen one major flaw in folks explaining, and inspecting these units etc.
Most, if not all, folks have never seen or inspected a new and undamaged unit, so they have no reference point as to know what feels/looks normal.
I’ve removed too many seized up units that the owners felt were normal (they all do that) not knowing they were on the edge of having their bike lock up the rear wheel and toss them off.
Folks think 1-2mm of movement is normal, yes, but are they really feeling free movement, or dead space because the piston is stuck in the bore etc.
If you want to see if your feeling pressure, or damage, place a bleed hose on the PCV, open it up to relieve the pressure, and see if you can then move the piston it’s full length.
Most folks are surprised when it still won’t move more than a millimeter or two because it’s stuck etc.
And yes, even when the piston is stuck in the outward end of the bore, you can press hard enough to stop the wheel, but that does not mean it’s working properly or safely.