It's a small business run from his garden shed Nice chap though, knows his stuff.

Anyway, back on topic, I bought two new sensors from ECP, they seem to have gone up, £68 + VAT each now. When I got around to removing the old ones it seems one has already been replaced. The driver's side - the one causing the error - is definitely the original, while the passenger side is a gen BMW one but looking much newer. I fitted both of the new ones anyway. I just have a spare now.

So far no more errors, and although I might be imagining it, the car seems to run smoother and pull more cleanly. Time will tell on both fronts but for now I'm happy