There is a small plug in the cylinder right at that spot. See the small allen screw right near the leak? That holds on that small cover, the plug is behind it. I'll bet you see the leak coming from there. It's been a long time since I messed with that part of my bike - but I recall I had the same leak about 20 years ago.. The little plug (brass, I think) was able to be removed by screwing the top of a spark plug into it (Take the screwed on part off the plug first, if it's there. The little thread is a perfect fit. Then just wiggle & pull the plug out. You're gonna lose coolant. Get a new one, put a bit of RTV on it, and gently tap it back into place. If that's where it's leaking from, it should be fixed...
EDIT: I left for a minute to find the part number for this little plug... 90338-11152-00 "Plug Special Shape". Costs about $4.50 each (From Ronayers.com) The bike uses 4 of them
Second thought: I believe I slobbered some silicone (or whatever I used to seal the plug) around the outside of the plug before I put the little cover back on. Maybe to have a bit more sealant there, I don't remember (Hey!, I'm OLD!!). In any case, it never leaked again, and totally forgot about it till I read this thread.......