There have been a lot of similar reports recently from the US with Standard Leslies and even Tone Generators!
It seems that the oil gets quite thick, even tacky in the cold.
My first thought is to try spraying the spindle the Drum spins on with something that'll get the thing eased up.... CRC, WD40 or something.
There are motor and belt adjustments we can look into later.
OH, does the slow motor spin with the belt removed? That'll let us know what state the oil in the slow motor is like....