Well, the long story cut short is that the van came back, it transpires it really is an M9R (not F9Q), the other injector at the O/S of the engine bay was also knackered (as per previous multimeter resistance measurements) and that took a week to pull. All work done previously on this van (before I saw it) was done incorrectly, and this meant that the injector coding was wrong for some time whilst the van was being used for two years since its first injector change (on cyl.4 over the flywheel). I now know that the main cause of problems for my interface with the EDC16 CP33 controller (not EDC15) was due to the Autel DS708 - it basically treats the van as an F9Q engined vehicle. I suspect that the previous repairer had the same problem. Tech2 and VauxCom both deal with the engine config and injector coding faultlessly.
Everything is now fixed, and the suggestions from GRUSS regarding the primary cause of failure (in the design of the screen decker rail seal) were absolutely bang-on. The seal was totally inept (anything else would not befit Renault's reputation for "Va Va Doom") and was directing all of the windscreen run-off straight over the engine at Cyl.4 (flywheel end) and under the cam-cover. So a new arrangement has been devised, and hopefully the van will give many years of good service now that some of its design faults have been tackled!