Well, after 100% (both) of the heater matrixes for my car turned out to be leaky and/or blocked I've taken the plunge and ordered a new one to be made to pattern including the mounting flange. The original is going off as a pattern part for them to use and I'll report back when the new one arrives and post some pics of the assembly in the airbag on my build thread.
I have also asked them to give me a price for a batch run in the hope of getting the price down a little. My quote is £150 + Carriage + VAT so it's going to be around £200 all in. With peace of mind for the future.
If anyone is interested in a new heater matrix please let me know in posts on this thread. I'm happy enough to organize a consortium for this one and not to make a profit out of it (other than the reduction of my cost to the unit cost for a bulk order!).
Guy