Lee

the bad news first - to replace the centre pod is not only definitely a dash out job but its the most difficult pod and normally requires removal of also the heater box components (evaporator I seem to remember).

I did a full dash out (see the pics on this link http://photos.wanadoo.co.uk/album/1259925) not long ago.

The centre vent pod is buried so deep I could not get at it without removing some of the heater box which I was not up for. In the end i tried a trick which I found on a forum which said you could remove the metal flap for the centres by bending it upwards and pulling it off. Then reaching in with a small hand and removing the pod. Well you can see the result on my pics - I did get the pod out but not without completely wrecking the flap for the centre vents. In fact this is not so bad as its the least important as you can switch them on/off manually using the wheel on the outside. So I now have full air permanently to centre vents and control them manually - fine really.

If you are happy with this solution and really dont want to spend six hours removing dash you could attempt to immobilise your centre vent flap by working throught the vents thus resulting in same situation I now have - manual wheel control. This is just an idea not something I have done so its entirely up to you. If you did it you would have to remove the centre vent assembly (see my pics) should only take 20 mins. Then you will see the top of the metal flap either horizontal (closed) or raised. If you lift it you will see the linkage pushing it up. You could try disconnecting it somehow and jamming the flap up or pulling it out completely. This may sound drastic but removing the dash still wont allow you to do the job without some disassembly of heater box (far too much effort in my view to when i can just use the external wheel on the vents instead).

Hope this gives you food for thought, sorry the news isnt better . I cant comment on how likely the pod is your problem but it does sound like it from what you described - have you checked the vacuum from the valve to all the pods - I would definitely do that first before embarking on any podectomy work , it could save you much time and pain.

let me know how it goes
Keith