Sorry to hear of your trouble. The RTE stands for "Renault Technical Expert" and he is basically what it says he is apparently he knows more than the regular technicians. Ihave to say this is true because whenever I've had a problem with mine the same RTE at Renault Manchester sorts it know problem.
I think its poor form for your dealer to say it hasn't got this and hasn't got that , I would recommend going to a Renault UK dealership if possible as they're the biggest and will most certainley have access to the
upgrades and a RTE.
I had a
fuel injection upgrade on mine at 18000 mile service which did help on mpg
WHat there saying is that there just not qualified to fix your car.
Sorry can't help any further but I wouldn't buy a new
just because of your dealerships poor service before trying all other avenues.