To clarify, are you also using Apple Mail?
Could you add the script to the Scripts menu (i.e., place it in the Scripts folder) in Mail?
I too am a very satisfied long-time user of SpamSieve.
Yes, Ira, I am using Apple Mail.
Re the placement of the Script, I did not have (all) the necessary folders (~/Library/Scripts/Applications/Mail) so I had to first make 2 of them (Applications & Mail) and then put them in the suggested locations.
Once that was done, I merely copied the compiled script to the end location.