| Hmm is R4 10w40? and does it happen if the R4 is fresh in the sump or after its had a few k miles through it?
If you get low oil pressure regardless of oil age,i.e its conditions related then I would fill with a 15w50 (full synth) so see if the higher viscosity keeps the oil pressure up at idle and hot temps, tje full synth will delay viscosity loss over time.
I think Castrol use mineral base oils tweaked to be "synthetic". High end Silkolene or motul oils use a true ester base synthetic blend (check back of can and look for Ester base statement) these will hold viscosity far better under stress than a mineral or mineral based synth. Hope that helps
PS if you've still got Oil light flicker at idle with the oild change then get a new oil sender before you worry about worn out engine internals, they do fail with age etc. | 
Hybrid Mode
