So I had this problem a while back and the only place that appeared to have it was round the header tank. I replaced that and the pressure cap £35 and the guy never charged me labour as he’s my local guy. Anyway a few weeks later there was more leakage there and we replaced the tank as it appeared to be coming from the middle of it rather than a join. No issues for about a year after that. Recently it’s started back up again and then sometimes it’s fine and sometimes it’s not. It’s been pressure tested and the mechanic had it up on the ramp and couldn’t find a leak he also left it running with paper underneath it (the engine base cover off obviously). He also said there was no obvious leakage there. What’s everybody’s thoughts?