Aye Pat,
Just don't mix castor R30 or R40 with mineral or semi-synthetics or synthetics. Synthetic to semi-synthetic with filter change, fine. Same with mineral.
Shop around for your oil as well. I'm still able to buy 20l 10-40 semi-synthetic for £20 + VAT. Same thing with a different 'brand' name at another factors £34 + VAT. As for motorcycle special oils in thumpers...... get a life!
Sorry to be crabit, but I've got the lurgy and its sleeting and the hot toddy + paracetemol hasn't kicked in yet!
May the sun shine on all your backs tomorrow and thumpers thrum with joy! It's catching Pat.
Cheers, Bill