It is a 42mm Festoon bulb, I originally replaced mine with the led equivalent:
Festoon 42mm 9 LED
But since then replaced the whole unit with a similar size LED enclosed unit which gives more light.
The RNLI have over the years run awareness campaigns regarding maintenance etc and even used to do safety checks, this was based on their callout engine failure stats.
I too had a bolt sheared off the steering pump that took out all three belts, although I couldn't fix the bolt I had the spare...
In my experience, I wouldn't bother with zinc spray paint, it never lasted that long, I found few coats of hammerite smooth silver paint more effective which I apply annually. As for rust, I generally use kurust which works well.
Have a look at the seago lite range, I bought the 230 model last year and so far no complaints, it stays on my snap davits with a cover to protect from UV. I also considered Crewsaver but not so easy to fit on snap davits.
You might find this dinghy review useful: Best inflatable boat: 9...
Yes patio magic will reduce the windows life, the same when using fabsil treatment, I learnt the hard way many many years ago. Now, I still use those products but with a paint brush and very careful along the window joins, not been a problem since. The worse is if your neighbour gets carried...
Interesting, I have just installed a new transducer and although I didn't need to make any changes to the transducer cable, I noted the instructions mentioned you can extended the cable with their ready made cables, how does this fit in with cable length and timing.
In my experience I've never trusted the NASA BM battery % readings and pretty much ignore it, instead I focus on the voltage and amp readings, that tells me all I need to know.
If you have to replace the thru hull fitting, check the sealant curing time, some state 24 hours which would be a problem overnight/launch, but saying that I think most are 12 hours curing time.