Aye Pat " semi synthetics are ok , even fully synthetics, The old problem was with mineral - vegitable [ castor based] they had a habit of conjeling, i raised a Topic on another forum , and everybody just mixed & matched, what was available [ tesco"s- rock oil- carlube -CastrolTT, ] all semi synth, there all good oil nowadays,
Oh i did a mix in glass , to see , with The famous Castrol R40.and rock oil semi-synth, it turned blackish purple colour, but never conjeled, after weeks , i used it in stihl saw ,