Who would you expect to do it?
Maybe you can ask them to change you more for them to repair or install?
Though if they suggested this option, i doubt they will off the service
If the soldering was bad, you would have a fault ages ago. If the solder was that crap stuff that comes away quite easily, its wear and tear (considering it was good for three years).
It seems you are adamant that the fault is with them and you deserve some form of compensation or something from them, but you have no idea about the fault. If i were in your shoes, i would look at it as if i had broken the item myself and would be either looking to repair or replace it myself, at the cost of my own time and/or money.
That's just it. No one knows what the fault is (okay so TM have a good idea) but the retailer doesn't. All I'm asking is that they at least review the case and not cut me off.