the grey oil at the start was a sign of metal to metal wear.most bearings failure is caused by rust which in most cases is the result of fuel left in the engine.alchol left in the engine will absorb any moisture in the air and after the alchol evaporates the water is left to cause the damage.nitro is also a contributing factor as it is a derivitiive of nitric acid and a corrosive and has a tendency to remove oil residue before it evaporates.this is one of the reasons for running your engine dry at the end of the day and what started the use of after run oils.