I can't really say much about the RP, our lab here at work to my knowledge has never tested any...used or new. I like Castrol, so much that I could get all my oil for my oil changes for free here at our oil plant, but choose to purchase Castrol anyway.
The Lucus, if you're talking about their oil additives, take a minute to think about this...if RP is supposed to be any good, why must you use any additives in it?
Oil companies such as the one I have worked for the past 13 years, spend millions in producing quality blends with the proper additives and quality base oils, so that they work properly when used accordingly. Adding outside elements to those oils drastically changes how the oil performs.
Out of all the emails we get here from pissed off consumers saying our oils contributed to engine failure, I can guesstimate that 95% of them had nothing at all to do with the oil they used, but what they chose to add to it or simply they misused the oil in a fashion not according to the label.
In my opinion, there isnt really a such thing as a "bad" engine oil in this day and age...motor oil's have come way too far in the market to actually be considered bad. It doesnt really matter if you are using Kendall that Jiffy lube filled your crankcase with or you spend $80 an oil change for Amsoil...what matters most is you follow the manufacturers recommendations on how to properly maintain your vehicle according to the service schedule your driving habits suggest.