Yanmar 3GM30F Oil Leak

[Capt.Don]

My 12 year old Yanmar 3GM30F, with about 500 hours, has developed a minor oil leak (about 1/4 quart per 4 hours or a couple tablespoons each time used). I'm looking for advice on the location of the leak, how I can find it, and whether this is something easily repaired. Here's a picture from the front of the engine after about 1/2 hour of moderate use,



The two things I've noticed are (1) there appears to be a very small bit of oil building on the lower front-left oil-pan bolt (small drip on right side of photo) and (2) a more sizable leak from the left-rear part of the engine. For clarification, both are on the left (oil-filter) side of the 3GM30F. The rear leak looks more significant.

Also, does anyone know the torque values for the oil-pan bolts? I'm hopeful this might be the cause, so I'd like to retorque the pan-bolts.

Any suggestions are most appreciated. Thanks