That should be the neutral switch. The oil level switch is further back on the pan, more toward the center. The oil level switch has a pigtail coming out of it, where the neutral switch just has a single wire attached by a crosshead JIS screw. Degrease it and find the weeping oil. The exhaust collector has to be removed in order to get the sensor out. The collector is difficult to remove with the headers still in place, and pretty impossible to remove separately if it's been on long enough for rust to build up around the gaskets.