What's this leaking?

Hi all. I've had my 2002 disco II for 2 years now. It's developed an oil leak and I have traced it to the area in the picture. It looks like an oil pressure switch but I have my doubts. It's located in the drivers side, just under the rocker cover. I'm beginning to wonder whether it is an oil leak now and perhaps it's diesel.

Anyone know what that switch is? :whoosh:

Usual leaks are

Diesel from the FPR at drivers side towards the rear

or

Oil at the front of the rocker housing from the big plastic bung

Many thanks for that. I'll give it a go

the one in the picture is deffinately the FPR...quite common to leak(diesel) ... put a new OEM one, the repair kit is not the best fix in most cases