Contacted the trader and he said I need to check the warranty. Warranty covers up to £500 of stereo repairs, which we know isn't going to cover the cost of replacing it for another ml unit. When I mentioned that I would take it out and try and repair it, he said he knows someone that repairs them and will contact them Monday morning (assume he means auto electrician).
I don't mind loosing nav functionality if I replace the head unit as I tend to use my phone anyway as the maps are way more up to date. How integrated is the head unit to the rest of the display? What functionality would I lose?
I've seen head units on sale on eBay but most seem to be from left hand drive cars in the US or Latvia. Costs are between £200 and £400.