940 Non-turbo

I wrote here last week about my O2 issue that Steve and others have given valuable help to me. I'm following up with my latest observations from the tests made and need further help to cure this perpetual problem.

I did the continuity test from the wire end to the ECU pin #24. The meter did not stay stable but I did get continuity. Perhaps it is my multimeter, which i bought cheaply.

Upon that I closed everything up, and sprayed some WD40 to the wire terminal (not the ECU end) and plugged back the O2 sensor connector. I know I should not but I was getting frustrated. The car ran some 800km without the check light on. Then it came back. I reset the ECU and ran another day without problem and thereafter it has been coming back and resetting the ECU and it stayed there for a day only come back the next.

What's next to do. I read that O2 can give expensive problem like clogging the CAT if not rectify early. I can't bear to fork out more expensive repairs.

Thanks in advance for you advice.

Regards
Laozong