Deck Light H376
The one on my '96 H376 is a horrible open fixture with no glass to keep the weather out. It was always failing.
However I found that the small size 12 volt 20 watt sealed beam low voltage dichroic downlighter lamp fitted it just perfectly - as used in domestic applications at home.
I think I used the MR16 as a replacement 2" diameter type GU5.3 or it may have been the smaller 35mm diameter one with a glass front cover type GU4. Sorry I cannot remember. The point being that it fitted the existing hole exactly. Also being sealed beam there was nowhere the salt spray could get in. Having only recently been up the mast you will probably remember whether the hole is 1 3/8" or 2" and you may well already have a spare one at home.
It was necessary to make connections to the bulb's pins which I did by removing two connectors from a 'chocolate strip' connector and screwing them directly onto the bulb's pins and separating them with a small piece of PTFE tape. The beam down on deck is marvellous.
All this was 8 years ago and still going strong.