SL-5 doesn't have similar auto return adjust screw as SL-7. I've read few threads people having similar problems, but didn't manage to find a solution.
I have the SL-5 (and SL-7) service manual(s), and it doesn't say anything about adjusting auto return. Looks like you can only adjust the start position! I opened the tonearm motor cover, but didn't manage to do much;

