Recently, every now and again, I had noticed what appeared to be a slight oil leak running down the crankcase cover from the bottom of the fairing.
Couldn't work out where it was coming from but as I was getting an occasional whiff of petrol, I assumed it was coming from a dodgy breather pipe.
Problem solved today when I discovered a blister in the paint along the bottom edge on the right hand side of the tank.
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Must have been a pinhole leak that only lost fuel when the tank was filled. Some fuel would leak out, run down to the lowest part of the edge and over the rubber seals on the fairing panel.
Then it dripped down on to the top of the crank cover.
Because it had melted the rubber a bit, it looked like an oil leak.
Had a fuel leak on my last K on the left side, where the fuel pump lives. Think its rarer on the right, but obviously not impossible.
If you get a whiff of fuel, check along the bottom edge for blisters in the paint. If you are far from home don't poke it!
It can turn into a big hole very quickly.
Easily fixed with epoxy putty.

good find cj

I just fixed a similar leak, although when I had emptied the tank and started to fiddle with the paint blister, I was horrified by the eventual size of the hole that appeared. All fixed now but haven't repainted the patch, and probably won't. Good reminder mate.
I may be in the market for a new tank as I don't want any more leaks.

It was a bit baffling because the 'leak' didn't appear at the same time as the smell of fuel.
As our K's move in to the classic bike world, maybe we need to think of a preventative measure like a tank sealant.
Might prevent those pin holes developing into something bigger as new or sound tanks can only get harder to find.

I had the same trouble with my 89 RS.  Hole under the fuel pump.  NAPA sells a epoxy kit specific to gas tanks.  Buy tow, do one inside and one outside the hole.  Warning it sets up really fast after you mix the two parts and it gets HOT.  Works like a charm and then I painted over it with a little matching touch-up from NAPA!