Valve guides. Classic. Unlikely to go bang but will just use more and more oil, and in time will start to detonate due to excess oil in the combustion chambers. Best get it seen to sooner rather than later, however you've probably got a few 1000 miles left in her.
Concur with that. I had the same thing, used about a litre of oil every 500 miles and cans were very black. Solution was a rebuild by TVR Power - could have been just the head, but one liner had slipped slightly so had the full rebuild. Runs nicely now........
