Firstly, please accept my apologies to not having reacted to your postings. Entirely my fault; lost a bit of motivation after all the negativity I have had with IWC and their local agent, so had not been following it up.
I have had contact directly with the factory in Schaffhausen who informed me that they cannot (or more likely will not) service my MARK XV, and asked that I deal with the local IWC importer (who are the distributors for BENELUX and Scandinavia) through one of the retailers. In desperation (and as the watch was now loosing a couple of minutes per day), and despite all the troubles that I have had with them over the years, I relented and sent the watch to them via one of the local retailers here in Holland.
The watch was away for almost 3 months for a routine service.
It came back almost as I had expected, serviced and cleaned, though without the new strap that I had requested in the original order. The watch was returned without any official IWC documentation (only a receipt from the dealer which I was told to keep as the one-year Warranty). Only when I called the Importer directly was I provided with official IWC documentation for the Service, and a 2-year Warranty.
All this has knocked my confidence in IWC somewhat, and made me re-consider my intention to pursue a 3233 (Ingenieur out of the Vintage Collection).