I think those problems went away long ago. IIRC, Pennzoil 10w40 had the worst reputation at the time. FWIW, that was the oil I used at the time, I never observed any problems or sludge from it but I'm a bit of a maintenance nut. I have increased the oil change schedule on the newer stuff up to ~2500, 3000 miles so I'm getting a bit less obsessed these days... but now that I work from home the 300 gets an oil change every year whether it needs it or not...