To chime in, I too have had a spurious (excellent description, by the way) alarm on my 2006 4.3l tks mercruiser. I chose to just throw parts at it, as I have no maintenance records for this boat and figured that replacing components wouldn't hurt, although some might consider it a waste of money. Fair enough. I replaced the oil pressure sender and switch, thermostat, water temperature sender and switch, and gear lube reservoir. Still got the random, intermittent alarm. What solved it for me was cleaning, dielectric greasing and reattaching the 9 pin connection where the main wiring harness joins the engine. A mechanic friend of mine had mentioned that the pins inside this connection were split down the middle, and the hose clamp that is around the shroud needed to be sufficiently tight to ensure a good connection. 30 hours of operation later and not a single peep from the alarm other than the initial tone prior to starting when the key is switched to on, which I understand is normal operation, as oil pressure is nonexistent at this point, and Mercruiser manual indicates this is to show alarm is operational. Just my .02.
