what are spark plug tubes and is this park of spark plug replacement?

They are sandwiched between the valve cover and engine block.... Valve covers have to be removed to replace the tube SEALS, tubes themselves should be ok!.... Not uncommon for these seals to leak oil into the tubes and onto the spark plugs... This is NOT done with routine plug replacement!..... Can't give you a price on tube seal replacement but the repair shop of your choice can!