You could always build back in a demister
http://www.cbsonline.co.uk/category/Heating__Air_con_and_Ventilation/Demist,b.html
Yes that is what I suggested I would do on the other thread, one or two MOT knowlegeables stated "no need" as far as the MOT is concerned.
I shall fabricate something anyway as it is not handy when in dire wet you are forced to put the roof and it dribbles over the top rail and collects on top the dash area. Udder wipes are very good for the cascade but on the +8 the vents helped dry out the rest. The Sport suffers in the same way ( not into bolting odds and sods of Neoprene everywhere as effective and innovative as it is)the minimalist look of the Sport compared to the +8 is what I want to preserve. What's a little bit of water in the cockpit anyway - my father who was a Spitfire pilot in 318 squadron used to take me for aerobatics in Tiger Moth's and Zlin's - by far and away the favourite was the Tiger complete with the rain in your face and up your everywhere, pure adrenalin pumping. He was CFI in three Flying Groups in Norfolk at the time and he was nuts in an aeroplane. Sadly he passed upwards at 64yrs to join the angels and old comrades and adversaries that he shared the space with a long time ago.

Quite a digress there sorry - they don't build men like that anymore although we owe it to the fallen to go like -hit and burn burn burn that petrol. The kids can play with battery and Hydrogen - What am I saying there

It is definately the £140 laminated localish Exeter fix - or as Ivan has suggested plant glazing / agricultural machinery suppliers.
Training event for the next couple of days but hopefully do a bit of research after that.