Be extremely careful when removing glow plugs from any diesel engine equipped Volkswagen vehicle.
If the metal casing becomes separated from the ceramic portion of the glow plug, the glow plug tip may be left in the cylinder head and could fall into the combustion chamber.
Obviously, if this happens do not crank the engine. The cylinder head must be removed to retrieve the tip.
While the head is off, inspect the piston, head and cylinder wall to verify that there is no damage.