What is this and why is it leaking?

[worldgnat]

Well, I finally found my oil leak the other day. It's coming from this little plug-looking thing just up and left from the drive sprocket. I don't recognize it, and can't find it in my Haynes manual. Can anyone tell me what this is? (Sorry for all the purple; I didn't have the forethought to take a picture during the day or with non-UV light.)

And, for bonus points, am I going to have to pull apart my crank case to stop it from leaking? Because that would be unfortunate...

 

[YamadudeXS650C]

There are a number of threads mentioning this plug, here is one:

http://www.xs650.com/threads/what-is-this-plugged-hole-for-72-engine-case.21421/#post-208576

 

[YamadudeXS650C]

Seems to be a vulnerable area in the left case. Damage and leaks happen when there is a catastrophic chain event.
Some have been successful sealing the area with JB Weld.
Some have had the case actually welded when there is a visible crack.

 

[worldgnat]

Hmmm, alright. I'll probably give the JBWeld a shot. Thanks for linking that thread; I haven't had much luck searching for this so far.

 

[YamadudeXS650C]

The success of that stuff depends on very thorough cleaning. I suggest using brake cleaner.
You'll get some additional opinions, soon.