I gave up on the old motor oil as bar oil when I had to replace the first oil pump and started using standard bar oil.
As for the mix, I can't bring myself to believe that 50:1 is enough oil, that's why I started mixing it in the tank. I first started by adding a little oil into the tank with the mixed gas then I quit mixing the gas and just started adding more oil to the tank.
I might just start mixing my gas 25:1 that way I know how much is in there.
Anyway, my point was that the 455 is a great saw, has suffer under 8 or 9 years of abuse, and still performs excellent everytime I get it out. It always bugs me when people talk about their, for example, toyota truck's durability when the truck has never been off the pavement, never pulled anything (or even been at full throttle for that matter), and has been regularly serviced every 3,000 miles. Of course they were able to put 300,000 miles on it, let me drive it for a few years, cutting firewood back in the woods, pulling tractors around, stomping it at every green light, and getting it serviced when I have time and lets see how long it lasts. If I get 300,000 miles out of it then you know it's a durable truck.