Hi Dan the cheapest option is to have a remap that ksps out the adblue system. That way you won't have a problem with the system again. The remap should cost between £200-500
Try osram night breaker bulbs.
Wet on the inside I'm assuming?
If so I'd check that the rest of the carpets aren't wet. Then I'd check the scuttle panel where the battery is for blocked water drains at the bottom of the battery tray. Also check if water is getting in via the pollen filter housing.
Is the warranty with them or through a third party?
If purchased within the first 6 months it's responsibility of the dealer to prove the issue wasn't there when you bought it. After 6 months it's the other way around. This applies to all goods purchased with new or used.
Oh I'd trust eBay. eBay are always on the side of the buyer not the seller. Plus if you pay via PayPal then you've got extra protection. I've been buying from eBay for 10 years bot not had an issue.
Doesn't matter if it's main dealer or not, all dealers have to comply with the sale of goods act.
Did you put petrol in it?
If not then it sounds like they're fobbing you off.
Service history is key. Ideally it should be full service history. Check for proof of cambelt and water pump changes as well as s-tronic gearbox oil changes and oil changes for the quattro system if applicable.
Check YouTube for buyers guides.
Make sure all electronic items work as some of these such as AC components etc can be expensive to change.
What a bargain!
Be careful regarding air bag wiring though as connectors can vary.
As such, if conne tors are different the easiest option is to change the airbags abs wiring from your current seats to the new ones believe it or not.