Assuming he checks out okay with the vet, some other ideas --
Was he neutered? Sometimes coat texture/quality can change after spay/neuter.
Are you running the heat more? You might add some moisture from a humidifier.
What's the fat content in the food they're eating? I like higher fat foods like 30/20 or similar for Labs.
Make sure to not just run a curry combo (like a zoom groom) over him, but to use an undercoat rake (not a furminator, that's damaging) to pull out that dull, dead, often orangey fur on chocolates. That will help.