Hi Toby,
I've experienced this issue twice with another manufacturer's lights.
The first time my expensive waterproof light started to collect moisture on the inside of the lens and after a few weeks it quit working.
Contacted the manufacturer but the light was out of warrantee so had to buy a new version.
The new improved redesigned expensive waterproof light started exhibiting the same issue so popped it open and sprayed the internals with a small amount of Boeshield T-9 and left it open to dry.
Upon reassembly, lubed all entries to housing with vaseline.
Light has been working flawlessly for almost a year and to prevent water egress into electronics, I now wipe vaseline over entry points on a regular basis.
Can't say this will be the solution for your case, but it certainly saved my equipment from ruin.
Semper Birotas!
Marvin
San Diego USA
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- Marvin Davis
Semper Birotas