1991 Chevrolet K1500, 4.3 V6. I want to run a thicker oil due to oil burning caused by bad valve guides. Truck is a beater but runs decent; gets me from point A to point B. Brand doesn’t matter. I didn’t have any success in finding a cheap 5W/40. Wondering if I should run a 10W/40 or just run 3 quarts 5W/30 and 2 quarts of 15W/40. Please advise.