Only pullin yer leg birdy... 5w30, 10w30, 5w40, 10w40, 15w40... mineral/semi/fully all suitable, wouldn't recommend 20w50 my mums, but that said it prolly wouldn't hurt it!
Just done nippers Ka on 5w30 semi (or was it 'part' synthetic?)... it was like piss!

And that being and old design motor didn't really need it, 10w40 would've been better (the 5w30 was cheaper!!), the protection comes from the synthetic side of oils, mineral oils are ok for door hinges!
I'm suprised that some older motors on 5w30 don't get the odd flicker of the oil light at low/idle revs!