Discounted Westerbeke?? That is an oxymoron. Good luck, do not be surprised when the dealer parts guy arrives at the counter carrying a jewelry scale. They sell by the Troy ounce.
Take the old filter, hit various Diesel engine dealers, forklift, farm tractor even auto parts stores and so forth to see if you can match it up. Try to, while you are at it, find out what else your genset engine is used on. Tractors, pumps and so forth. There are casting numbers on the side of the block that may help. Good luck...BTW share any knowledge you acquire on here, it will be appreciated.