We got the car back yesterday - the diagnosis was "missing sealant on the bulkhead", I couldn't chat to the people who did the work to get specifics but I'll have a poke around on the car over the weekend.
Obviously the water was getting in there, pooling up somewhere and then moving to the rear of the car when parked on the driveway at a steep angle, odd how it was only in the rear when we first noticed it on the flat though.
Anyway they reckon it's sorted - carpets removed and dried out, all the foam underneath replaced and the car valeted, I can't fault the work so far if it does prove to fix the issue
Sadly they let themselves down with the courtesy cars.
On arrival on Monday morning, almost a month after booking the car in, my partner was told that someone else had been given the car reserved for her. They opted to get another car from their other dealership which meant my partner was almost late for work. The car was a previous shape Punto, filthy windscreen, vapours in the tank and, as we realised that night, without a valid tax disk! Nice to drive though, I preferred the newer black interior to the grey one in our old ELX 16v.
So the car went back and was swapped for a Grande 1.2 Dynamic in silver, lovely colour, contrasting light blue seats and dash trim (potential for dirt though) and felt about the same to drive as our 1.4, for the savings available on this engine it's definitely worth considering over the 1.4 8v. Sadly the car, despite being new, wasn't without a fault, apart from the usual lack of petrol (needle didn't even move when we started it up) the heater fans only worked on number 4, the other settings resulted in nothing.
All in all a decent enough experience for a Fiat warranty repair but it's clear they still have a fair way to go on the service side of things unfortuntely. We asked about swapping the car for something similar in 16v and despite the dealer principle saying he'd help out to compensate for our woes the offer made was offensive.
So we'll either hang on to it for a while or try our luck elsewhere.