That's an interesting comment and no doubt dead accurate, that just taking it apart and putting it back together might cure the problem.
These Honda brake calipers are he height of simplicity; let me recount. The body is made in two halfs, held together by two bolts. One half holds one of the brake pads and has no moving parts. The other half is simply a block of aluminum with three holes drilled in it; one large and two small. The first of the two small holes is the hole where the brake line screws into the caliper and is how fluid is delivered (under great pressure) to the caliper and it extends into the bottom of the big hole. The second small hole is where the bleeder screws in, this hole also extends into the bottom of the big hold. The bleeder hole is there to allow air to be evacuated from the system as fluid is initially added. The big hole is the important one. It has to be very smooth and it also has a deep groove machined into its diameter to hold the "seal". A piston fits into the big hole and that piston is pushed from the rear by the high pressure brake fluid that enters through the first small hole when the brakes are applied On the front end of the piston there will be a small plastic free-floating ring* and then the other brake pad. And that's all there is to it.
If your brake is leaking there are only three places where it can be happening. Going back to the explanation above you can see it might come from a cracked caliper, which I've never heard of happening. It might come from a lose bleeder, but your's isn't. It might also come from a lose brake line fitting where it screws into the caliper, but your's isn't. Finally all that is left is that it might be leaking from where the piston fits into the big hole, and that's got a seal riding in the grove mentioned above. Because its the last thing left it must be your problem. So that was easy enough.
Now the seal. The seal in this case is just a square shouldered rubber washer, its about an eight-inch square and an inch in diameter. So, you pick the old one out of the grove, take a new one and lube it with silicon lubricant and stick it back in the grove, put the piston back in, put the whole thing back together, bleed it, and you're on your way. Also easy enough.
Now a thought on the seal. That seal doesn't actually wear out, it becomes inelastic. So often just removing it, cleaning it, moving it around and reinserting it with a different orientation in its grove will be enough for it to start doing its job all over again. Just like magic it sort of fixes itself because you laid on hands. Of course if the process of deterioration of the rubber has already begun the fix will be short lived, but it will buy you time. A new seal, by the way, can be had for ten bucks. Although I haven't gone looking for one yet I'd be almost willing to bet that the seal is a common item in the hydraulics trades and can be had for a lot less, but that's another matter.
* Often this ring will be lost, and if it is not replaced the brakes will squeal.
