I've recently bought this machined oil cap for the Rover V8 engined my Plus 8 and I have to say it's a beaut!
CNC machined from solid aluminium and polished, I'm really pleased with the quality, finish and, I believe, looks a significant improvement over the standard orange or nondescript black that these engines cam fitted with.
If you're interested, the cost is £29 and the contact is Richard Powell on 07718996538. I've no commercial or other relationship other than as an impressed and very happy customer.