Trans Leaking from Top (sensor)?

[rts9364]

I have a 93 GA with a 2.3 SOHC and manual trans. The trans is leaking on the passenger side of the diff. case. At first glance, it appears it would be the output shaft seal, but upon further inspection, the TOP of the transmission is wet with oil up around the fill plug and the sensor for (presumably) vehicle speed and/or the shift light. Am I correct in assuming this sensor is asscociated with the shift light and/or speedo? Also, has anyone experienced a leak in this area? I haven't disassembled yet to assess, but if I could find something out beforehand, that would be great. There's that possibility with a 15 year-old vehicle for a chain reaction of breaking parts when you start diving into something!

P.S. I just bought this car a month ago, so I don't know any history behind this leak. Thanks!