On re-reading this thread, I've just realised that David mentioned a secondary issue in his original post which I for one missed. In his concluding paragraph he said:
Winter is here and the heater on this particular car has always had a fairly restricted effect (especially compared with my 940 which is like an oven when on full) so it's often difficult to keep the screen clear with so much damp in there and I'm also concerned I'll have rotted the floor out if I don't get something sorted sooner or later!
Having owned both 7 and 9 series cars over the years, my own experience would suggest that there was little difference in heat output between the two models. I didn't measure it scientifically, or even have the house-hold thermometer in the car, but both were very efficient; much like the proverbial oven, David!
This leads me to question whether his engine may be running on the 'cool' side, perhaps due to a 'stuck' thermostat? Alternatively, cold air may be getting in - if there is indeed a leak - where it ought not to be, thereby compromising the heater's effectiveness?
If the car is presently fitted with a viscous coupling mechanical fan, removing it and replacing it with an electric one may improve the efficiency of the heating system. In conditions of extreme cold, fitting a partial radiator blind (piece of cardboard
) may improve things - but keep an eagle eye on the temp. gauge!
In Scandinavia I believe adjustable radiator blinds were available as an accessory and electric engine block heaters are also widely used - but they may be a step too far in our normally relatively mild climate.
Regards, John.