Might be simplest method to use manufacturer‘s warranties & recommendations; however, not very cost efficient. For example, I recently changed my engine mounts at 18 years; yanmar recommends5 years. I changed my Volvo shaft seal at 17 years; Volvo recommends 5 years (old one looked just as good as new replacement). In many instances, manufacturers recommend replace intervals to cover their rearend & to boost profits. Better method is to inspect hoses for cracks, rigidity vs flexibility, & appearance. I recently replaced my head & galley thru hull fittings at 17 years because of Beneteau’s use of lower quality OEM fittings; for convenience, I also replaced the 11/2” trident hoses with saniflex hoses at the same time. The original hoses appeared normal & would have lasted for many years. Now, if I were planning a major cruise to remote locations, I would be much more prone to replacement to prevent unexpected failure & to avoid problems with parts availability. So, my advice is to thoroughly inspect & replace as necessary. And, be sure to close those thru hull valves when not onboard..
