2005 Ford Focus Edge: Air getting into the engine via the engine breather hose

Hi All,

Symptoms:
1) Can barely drive up inclines
2) Mini acceleration surges at low revs (symptom does not appear at high revs)
3) I hear a hissing sound when the engine runs and I squeeze the engine breather hose (behind the manifold)
4) There were no electrical/sensor faults detected by the RAC

RAC have looked and stated that it was most likely a loose fitting (or wrong sized) hose and suggested I replace it.  His reasoning was that low revs do not create a good seal, but higher revs do create a good seal - preventing any air from getting in.

I am keen to do this, but my questions are:
a) Do the above symptoms indicate that it is an issue with the hose or PCV? (or something else?)
b) Are there any tests I can do to find out where the problem is? (RAC used a water spray to try and find a leak - they didn't)
c) If I do have to replace the hose, is it possible to do without taking off the manifold? (hose is at the front under the manifold)

The car:
2005 1.6 Edge
96K on the clock
Hasn't had any servicing in the past year

I can post engine pics if it helps.

Thanks for any help.
Pete.