LOST WATER PRESURE THROUGH P HOLE ON A 1982 80 HP MERCURY SER NUM 5705381 4 CYL. IS THIS HARD TO CHANGE OR EASY? WHERE CAN I FIND PARTS AT? IS THIS EXPENSIVE OR CHEEP ? PLEASE SAY CHEEP JUST SPENT 1400.00 ON BOAT ALREADY.THANKS FOR YOUR TIME AND KNOWLEDGE---------I SAY FISH FIVE DAYS WORK TWO DAYS----IF POSSIBLE.