oil leak 1.6 petrol

[niteram]

Hi, I've got a couple of Astra J's, both 1.6 petrol
one has started a to leak a little oil - it doesn't seem to drip on the floor but the sump is wet - the drips fall onto the exhaust while driving (I love the smell of burning oil in the morning)

I've taken off the manifold heat shield and the front of block is also damp, so its not the sump gasket or the head gasket.
Is it likely to be the oil pressure switch?
Is this a known fault?

[niteram]

I've just got it back from the garage,
it was the oil cooler seals leaking, the replaced them all with genuine GM parts.
It was due an oil change, so they changed the oil and filter and of course the coolant incase it was contminated