Ok so a 50/50 mix of Mobil 20W50 and 0W40 just makes the noise louder (yes the Mobil tech guy didn't see an issue with this....I've done it with air cooleds before). I've thus resigned myself to changing the offending lifter/s. After having a look at access for an "engine in" job I thought an engine drop might just be easier until I watched a 3 part series Youtube video of the whole procedure
There is a lot too it. I'll spend a couple of hours and see how it goes.