With TOG's mileage there may be a build up of hardened sludge around the oil pick up pipe and around the inside of the sump, the last thing you'd want to do is loosen it off and then find that the oilways become blocked with that debris.
I'd just do an oil and filter change on her with the correct grade of decent brand oil.
Is the tapping from the top end (valve clearances) or is it injector tick ?
Hi RS, that's a good question. I'm not expert in this so may well be mistaken but it sounds like top end. When I changed the timing belt and had the camcover off I checked the gaps. Several were too tight according to spec so that makes me think it's top end rather than injectors. 🤔