wormin i would change them out for new ones .. If you keep plugs that long you should pull them out and reset the gap every 100 hours of run time but as for me i just change them once a year its cheep insuance and dont forget to keep a nice new set in the boat just in case . OH make sure to pre check and set the gap and put the tinest bit of antisize on the threds and stor them in a ziplock bag to keep out moisture . You will think me later..
Take the number off the plug you have now and call the auto parts store they keep some boating stuff now.