I always use the mercury branded dark green stuff, not sure why, I'm probly a mug. Made for them by valvoline. It has the advantage of coloured dye, so you know if you put it in. But I spect all the marine ones are similar, and many have the dye I believe the non-marine motorbike ones do not have corrosion inhibitors, so better to use a marine one?
Castrol R, apart from being the second-best smell known to mankind, is a racing oil. It's a vegetable oil with great lubricating abilities, BUT it breaks down quickly so it's not recommended for anything that doesn't require stripping-down every 30 laps. You'd be better advised to use a synthetic or semi-synthetic oil. But get some Castrol R anyway, and pour a cap-full into the fuel tank of your (non-fuel-injected) car or motorbike...the smell as it burns off is divine.
Have always thought that if Castrol brought out an aftershave called Castrol R Pour Hommes (or maybe they could call it Hailwood, or Ago, or something similar) they'd make a fortune from those of us who spent our formative years track-side.
Don't use castrol R in anything you won't strip regularly. It leaves a gummy deposit behind that builds up & up. Modern synthetics are much better & if you hunt around there are some sold for bikes that have the smell too.(almost) .
Used to be a well-known rumour not to use Vegtable based oil in anything that had used mineral based w/o stripping /cleaning first & vice-versa....supposedly it would create a thick gunge that'd block oilways etc.....think it's a wive's tale, but there you go.