I have always found it kinder to the mechanism to change gear relatively slowly, double declutching on both up and down changes. If I try to be quick, a rending crunching noise wakes the neighbourhood!
Bob, I use Penrite transoil 90 made for classic cars. . Only one source in the States, in California. My M almost never grinds and only down shifts require double clutch, the PA requires a double clutch up and down.I use Penrite HPR 40 oil for the engine. I think it is 25w-70! Great stuff, maybe 70 is too high in the frozen north where you live. Best regards