That is definitely odd. While his teeth may look good to you, it’s actually typically the back most teeth that cause issues and some drooling, and it is impossible to examine them properly without the proper tools and in most cases putting the rabbit under anesthesia for a bit. I would suggest going to an experienced exotic rabbit vet in order to assess what may be happening.
For both the short and long term, it will be important to find out what’s happening. With just the chin dirtiness and any medical issues aside, having a damp and dirty chin is a welcome territory for bacteria to breed, leading to fungal infections, so it is good that you’re investigating what it may be.
When do you notice his chin gets most wet? Do you notice him having any challenges grooming himself? I’ve never heard of rabbits having issues with those scent glands.
<hr />
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.