Six months? That seems a bit pointless, especially given the 1000 hour alternative.
Printable View
Changing the filters on those is kind of a PITA. I would change oil every 3-5 years and filter every other time if you only put 100hrs/year on them. You never stated how much you run them.
FWIW.. The 514c manual called for 9 gallons, but in my boat, it has the shallow case and only took about 6 gallons. I used shell rotella T1 because it was the only engine oil I found that said it was good for transmission service.