Is this a head gasket failure?

I feel like I only come on here to ask questions and don't contribute much, but I'm back again...
Reckon I've got oil leaking out under one of the head bolts - it's in the valley between the rocker cover and the inlet manifold. I can wipe the oil off but it's back soon enough. A couple of questions:
- I take it that I've got a head gasket leak between an oilway and the bolt hole?
- Does a leak like this typically indicate a warped head, or is it no more/less likely than any other gasket failure to imply that the head has warped?
Any advice gratefully received - thanks in advance.

<edit> It occurs to me that I could be being stupid and it's just a rocker cover leak. I'll have a look in daylight.

Which type of engine have you got?

With no other symptoms...smoke or oil in water etc. I would guess a rocker gasket leak more likely than a head gasket.

Ah, I did rather miss out that important detail. It's a 300tdi. The vehicle as a whole is an exercise in managed decreptitude (which Disco isn't?) but the only smoke is black when nailing it, and there's no oil in the water, mayonnaise on the filler cap etc. We're passing within a couple of miles of Paddock Spares tomorrow morning so will take the opportunity to get a new rocker gasket, washers for the rocker cover bolts etc. and will report back if the leak does / doesn't go away!

Of course, once the leak is fixed, the front end of the chassis will start to rust...

Rocker cover gasket now replaced (with a genuine part, just to be on the safe side).