I had exactly the same issue, in my steaming light did not work and upon investigation found deck light casing flooded with water (no idea where it came from and assume condensation over the last 15 years) and therefore negative wire connections for both lights useless.
The good news I am sharing is you can get a lense replacement from Hella lights via their spotlight range. Look for part number 1GA 007 506-011 Hella FF. It is exactly the same. You cannot buy lense on it’s own from car of marine Halla range, you have to buy spotlight. I found on various places for £30 and even found non-hella equivalent even cheeper (I chose to order Hella part to be sure).
You will need to buy replacement h3 bulb.
And the water problem, drill drainage holes into casing underneath to avoid repeat. Design flaw really, as they should be there already.