Rusty cylinder

[cerdad]

Got the heads off and where the motor has been standing one of the liners is rusty,an area about the size of a credit card, the valve was open i guess and let the damp air in. Do i replace or can it be rubbed back with fine emery ,if not how much of a job to change a liner.
Also the holes in the head gasket for water flow are small ,has anybody opened them up to allow the water to circulate easier or is it to preserve the integrity of the gasket that they are so small

[cerdad]

its just the one liner the rest are ok ,your patch is difficult to see ,mine is bout 2" deep and 3 " long