Folks,
This sounds like what's called flocculation. It's a known phenomenon with castor, and is common when it's stored in cold conditions. I've seen it a couple of times with some cans of Castrol M an old motorcycling buddy gave me - I keep them in an unheated garage. The cure is simply to move the castor into a warm room and leave it for a couple of days, whereupon the white flecks should disappear. No need to filter.
Regards
John