Ahh, the old "mechanic in a can" trick. I have never used any Lucas product, but it can't be much different the the old standby, when you don't have time or money to repair it right, you pour in a can of STP oil Treatment.
Used to call this stuff, STP
lease or S
uddles. It has the viscosity of bee's honey, on a cold morning, only thicker.
It won't fix the problem, only prolong the inevitable. Normal oil pressure for a stock, used, 258, is about 7 psi to 20 psi. Before I rebuilt mine, that is what I was seeing on a mechanical oil pressure gauge.
After my rebuild and a Melling High Volume oil pump, on startup, I see 70 psi and it will drop down to about 60 psi in a few seconds. When warm, and at hi way speed, I see 50 psi and around 20 psi at idle.
As for the viscosity of the oil, living in the South, I use 30W HD "high detergent" oil. Multi-viscosity oil is great also, but I find the the 30W HD oil keeps the inside of the engine cleaner and I change the oil regularly.
STP and Lucas oil treatment products are still on the market and selling well. So is radiator stop leak, power steering stop leak, engine oil stop leak, etc.
There is NO "Mechanic In A Can"...