ACDelco Professional 18E605 Front Drum Brake Wheel Cylinder

Does this include 1 or 2 cylinders?

Is there a left aand right or fits both sides?

What is the difference between the front and rear brake cylinder if the technical specifications are the same, some detail that I do not know

Are these made with synthetic rubber seals that can withstand modern dot 3, 4, 5 brake fluid? old european cars had real rubber that dot fluids ate