Oh oh. Another one of "those" sensors. Rubb I just fixed this on mine 3 weeks ago. It was about $90 for a new sensor and gasket. Mine was erratic too and when I researched the .org, guys were replacing the sensor or trying to clean it, but after seeing how much work it went into getting to the sensor, I didn't want to do the job twice if cleaning it didn't fix it. It looks like Suzuki knows about this because, when you go order the parts, there is an old part number scratched off and a new part number listed as the replacement/upgrade? For it. The sensor is behind the clutch basket.
Hope this helps .