The other possibility is a crack in the engine block or cylinder head. I don't think a leak-down test would be able to differentiate. The mechanic's camera might be able to see a crack.

 

After taking off the head, you can probably see evidence of the leak if you look at the surface of the gasket or head or block. If there's nothing visible, then maybe carefully inspect for cracks.

 

Even with a small crack near a water port, I'd think the OP would have noticed the cooling loss. Even if he topped the jug off say once a month, you'd notice it. Seems odd that only #1 cylinder is getting coolant into it (according to the mechanic), if the OP isn't topping up the system. Maybe I'm wrong, but if you have a crack in the cylinder head, it's either usually near a water port, or between 2 exhaust ports. And I don't think Honda designed the head to put 2 exhaust ports near each other.

 

I'd have it magnafluxed to look for small cracks that you can't see. A good machine shop should be able to do that for a small extra cost.

 

Update! I've managed to get the cylinder head off. It was definitely an adventure, removing the crankshaft pulley bolt was a pain in the ***. I could definitely see some coolant in cylinder 1, but I did not notice any glaring failures in the head gasket nor cylinder head cracks. I'll be taking the cylinder head to a machine shop tomorrow to get examined and resurfaced.

As for the discussion regarding the cause of failure, the car was not exhibiting any overheating. I was not having to regularly replace coolant. The misfires were only happening for about a week before I dismantled it. Misfires only occurred on cold startup, they never happened while the car was running or if I turned the car off and then immediately started it again. The current game plan is to replace the gaskets and o-rings, put it all back together, and test it. If the misfire problem is resolved I'll take it to my local mechanic to have him examine the cooling system.

 

Many years after... very interested in how did your story ended! (similar problem with my 2005 Acord 2.4 EX)