I doubt you can buy a bad oil these days providing it’s a recognised brand. The specifications will be printed on the container, as you well know, if it’s a top up & as the Old Oily Bugger says any OEM spec isn’t going to make a mess.
My Dad would only use Duckhams 20/50, he told me it was green because it had copper in it & that coated the bearings, reducing wear & I still don’t know whether he was having me on or not.
He also told me that Kippers were caught in the Leeds Liverpool canal & that’s why they were oily. That might shine some light on the subject.
M