The man from AKZO coatings told me once that once Sunkorite has separated down into its particulants, it is impossible (?) to reconstitute it. The give-away is generally, the use-by date. But a tin that well used and shaken will last well beyond that date.
Brian has the idea re temperature and thickness. But be advised. The temp is slightly beyond the melting point of soft solder so you might find a weep of solder between soldered joints such as the body pads, foresight blocks etc etc