a bronze strainer like a Groco or Perko it is likely cosmetic. If you can pull it out and take a look you may find that it is OK. You could polish it up to make it pretty but it will turn green again in time. You may decide to get new gaskets for it to prevent any leaks before you put it back in. Hamilton Marine used to carry parts. I put in a new engine last year and sprung for a new, bigger filter. They get pricey! I'd want be sure it's knackered before I replaced one.