Hmmm...well I've been using Castrol M for the last 50 years and never seen any glazing or had a clogged bearing (other than bearings that have sat idle for a few years). With the engine that I used the most, every hundred or so hours I'd clean the carbon off the piston crown and go for another hundred odd hours. It's still got the original bearings but I put a new set of rings in it after several hundred hours because it was taking a couple of flicks to get it running .