Do RELIABLE 12v LEDs exist?

If we are talking about an anchor light ie just all white all round, I think you can very easily cobble up something yourself. Many of the really cheap bulbs from China will be fine. Sure they are resistive current limited but then you are unlikely to be charging batteries when at anchor at night. And even under chargevoltage I wouldn't worry anyway.
As said the trick is to have the anchor light as a temporary thing so you never have to climb the mast to service it.Of course an LED nachor light should be incredibly reliable.
as has been identified it is corrosion that is the biggest killer. Unfortunately the leads on LED bulbs tend to be iron so rust very quickly especially being so thin. The surface mount bulbs probably are more reliable being soldered in. Provided the copper tracks on the Printed Circuit Board (PCB) are robust then you should be set for reliability. I think due to simplicity the resistive current ;limiting should be more reliable by simply having less components.
Then you have to water proof the whole thing. Epoxy encapsulation can work well.
One thing for sure higher price might indicate more reliability from better design and water/moisture proofing but ha tis no guarantee at all. So to the OP certainly LED must be more reliable than incandescent bulbs with problems or corroded contacts and filament failure. good luck olewill
 
I have soldered leds from the bayonet fitting so if leds break i can just put the original bayonet bulb in. I doubt they are legal but the colour and clarity is apparently really good from quite a distance.No problems so far and i guess they have been running for about 50 hours in total. ps.check polarity BRFORE soldering!!
I used these- http://www.amazon.co.uk/gp/product/B003RU2M88/ref=pe_54411_38961691_email_1p_7_ti and sprayed the whole lot with ACF50.
 
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