Might be the oil seal. Each camshaft has an oil seal at either end. I'll keep it simple.
The top of the engine, through which the spark plugs go, is the "rocker cover". It's called this because underneath it are traditionally "cam followers", which rock, each actuating a "push rod", which forces open a "valve" in the cylinder. The days of cam follwers are gone, replaced by newer technology ("hydraulic lifters") but the rocker cover name has remained.
If you look closely at your engine, you'll notice there is a very fine seam between the rocker cover and the cylinder head, with black circular plastic oil seals halfway between the two. Behind the seals are the ends of the camshafts, which sit in high pressure oil, so the seals are important because the camshafts don't use any bearings, they literally just rest between the rocker cover and the cylinder head with high pressure oil squished between.
They all leak eventually.
I would change the oil seal before before blaming the head gasket for the simple reason that you can change these without splitting major engine components apart. Especially since you are not noticing any other symptom for head gasket failure. Changing a head gasket is very invasive and rather complicated.
Changing an oil seal is much simpler. Basically the procedure is this: Remove aux belt, remove timing belt, remove the pulley, pluck out the oil seal, knock the new one in, then put it all back together again.
So that's where I'd start if it was me.
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