How do I put oil in my Rolls Royce?

I have a RR Silver Shadow (Mk 1) 1972. I know little about it as all servicing is carried out professionally, but how do I add engine oil? I have checked the dipstick and I need to add oil, but there does not seem to be an oil filler-cap to unscrew to top up the oil. Any advice would be gratefully received. - Phil.