The rocker cover of my Fiesta gets coated in a thick layer of 'salad cream' (which I assume is emulsified oil) very quickly (in a matter of weeks). It is now starting to block the oil filler/breather cap. The car is used 2 or 3 times a week for a motorway journey of 20 miles.

Is this a sign that the head gasket has gone or is there anything else it could be?

I am now having problems with stalling coming up to junctions as I assume the breather pipework is getting blocked because of this.