I have a 2010 sportster forty eight with 25 000 km and have noticed oil below the starter motor.

It is a slow buildup and thought it was from the breather but ok, then read and thought it was the seal between the two halves which can be a nightmare and big $$$.

Looks like its not that but looking from the left hand side below the starter motor there is a sensor which enters the reverse side sort of opposite and higher than the derby cover.

Can anyone please tell me what this sensor is and can it be tightened ?

I canot find any thing in the service manual I downloaded ? 

i think your looking @ the speedo censor , wash proper & blow dry when puff babypodwer all round the area then ride around the block  then look for the wet spot  , could be gearbox overflow tube 

 

Good advice,
I did that with a fat chick.....baby powder to find the wet spot.

worked a treat.......

did you lick the powder off the wet spot 1st