Just have the one cylinder done,send it to a reputable engine shop.Am sure Norvic will rework it for you.
I used to have a Pa28-140 ex CSE Oxford, with 4300hrs on the engine,ran great,made the climb performance when we used to have a C of A airtest every three years.
I think CSE used to have an excemption from the CAA to run their PA28 fleet engines to 5000hrs on the old Public Transport CofA.