been using Nulon 10W-40 hi-flow full synth for past 3 years. It's good stuff no complaints and cheap on sale at Autobarn/SCA I usually get it for around $40 for 6L. Penrite is usually more expensive but if you get lucky with a 50% off sale or something go for it. Maybe try a petrol additive like Nulon total fuel system cleaner or wynns petrol complete system cleaner. and yea valvo engine armour sucks it doesn't last that long stick to a full synth (on sale)