I emailed what car just to ask there opinion on the offer. Here's what they said.
Hi Andrew
Thanks for getting in touch with What Car? I'm sorry to hear about your Twingo problems.
A quick search on Google reveals a couple of forums with people discussing similar problems, but ball joint failures don't seem to be so widespread to be any more than minor anecdotal evidence of a common fault. Perhaps the fact that Renault has offered to pay 60% of the repair bill suggests it may not be a one-off complaint. However, Renault may be offering to pay this purely out of goodwill to keep your loyalty to the brand. That's certainly what it would argue, I suspect.
Considering that the car's now out of warranty, and that the warranty on the replacement parts has also expired, I think that Renault's offer is a good one and would advise you to accept it. The manufacturer isn't under any obligation to fund any of the repair so this seems more than fair.
You could try asking for more, though I doubt an appeal would be successful and although it's galling when any part on a car fails, especially when it costs you, at least you're not being asked to pay the full £550.
Best wishes
Emma
