Maf Sensor Dilemma - 55 Focus, 1.6Tdci Auto

Hi - would appreciate any advice on this! 1.6tdci 55 plate focus with 7 speed auto, 75k miles. No particular probs for three years, but it has developed a fault which is related to the MAF sensor according to the Ford diagnostic check. The symptom is at low revs and when gently applying the throttle or going up a slight incline, the engine momentarily dies and a big puff of black smoke comes out of the back. It's as if it is struggling to decide which gear to select. I had the MAF cleaned in the service and all was well for about a month, now it is at it again.

Bit of extra info: there is a film of oil on the air box which is blowing out of the engine breather which the mechanic reckons is not due to a leak, just a higher rate fo loss than he would expect from a car with his mileage - it doesn't need topping up between services or smoke much normally as far as I can see, so that may stand a second opinion. He reckons this may be the cause of the MAF getting dirty but not much can be done, and no prob if it just needs an annual clean. Thing is, it's becoming monthly!

So, I could buy a new sensor and see what happens - may not be linked to the oil? I could have another look for a leak - is there a 'classic' spot for this? Or I need a way of diverting the oil away from the MAF. Do you really need one in fact - maybe I can just disconnect it?

Any help much appreciated. I will report back on any results!