It appears to be little oil seepage from the O-ring on the shaft end of the starter. See picture below.
This shaft is lubricated by the engine oil in the crankcase so unless the leakage is enough to cause a noticeable drop in your oil level, it is not something to worry too much about.
If you can live with the cosmetics of this seepage, it can certainly wait until you choose to have this fixed. If you want to do this yourself, it is pretty easy. To remove the starter, take out the two bolts securing it on the right side of the engine and then just kind of wiggle the starter to pull it out. The O-ring usually secures it pretty tightly. With the starter out, clean off any dirt/oil and check the O-ring for any damage. If the O-ring looks good you could just reinstall it with a good coating of grease, or you could replace the O-ring.