Calm down! Calm down!
The lobe in the photo does
seem to have some wear .. but before you rush off to hand over £400 or more of your moolah, measure the height of the lobe and see whether it's within the wear limits. If you can shim the offending valve(s) up so that they open the right amount, the cam is still good.
There's no need to change it just yet... (or at all, arguably).
Don't worry about the oil history. The modern semi-synthetics last 12,000 miles according to the manufacturer so the long interval isn't too shocking as far as the oil is concerned. It's actually more likely that the oil change happened and just wasn't recorded.
The black oil is just carbon, gum and varnish being picked up inside the new oil. You want your oil to go black because that means it's absorbing the contaminants inside the engine. If I was you, I'd change it again since it'll put your mind at rest a bit.
Use 300ml of kerosene (or "engine oil flush" if you want a fancy label) in the hot engine oil... Let it idle at 2000rpm for 10 or 15 minutes and then let it cool and drain it. Don't drive the car with kerosene in the oil.
That will loosen up a load more black stuff.
Put a new filter on it too... let it drain for a very long time... refill with synthetic oil (0W60 for your JTS donkey...? ) as this has more detergents than semi-synthetics. I think AR do state the JTS needs synthetic anyway... but look in the book.
The clattery engine could be the variator but also check the valve gaps etc. They could just need the tappets adjusting.
Put that all together with a new cam-belt and tensionerator and see if the beast is much better or not...
If he's still feeling a bit weedy next year, then start saving up for some good cams and stick them in at the next service (12,000 miles?)