Second Oil Drain plug 17mm for the Stator Housing?

I did an oil change today on my 1979 KZ1300 with 25k miles.
I have a question about a second 17mm drain plug which I removed and about 5 oz of oil drained out. This I believe is for cooling the stator in some way.

This is the first time I opened that drain.
What type of circulation is inside that casing? Should this small amount of oil be changed, bcuz why have a drain plug?
Does the case fill up a little bit then stop filling? Does the same oil sit there until it is drained?
I have a manual. I was wondering if there was a fill port to add oil into the stator housing. But I think it gets oil internally, I just don’t know the process, and if 
oil that is inputed circulates with the main supply. Interesting Stuff!

The last thing I want to do is disrupt the stator or abuse it given the charging vs. problem not charging is a known fragile area on the KZ1300.
I appreciate knowledge shared by fellow KZ1300 owners!

Hello jftman,
Where do you see a second 17mm drain plug? The service manual mentions removing the 17mm drain plug in the oil pan and also the 17mm bolt that secures the oil filter cover. I suggest that you explore the 1300 section of the FileBase. You'll find a service manual that you can download there. 
There are, of course, plenty of knowledgeable members here at KZR but I suggest that you follow the link in my signature where you'll find a bunch of folks who focus solely on that bike.
Oh, by the way: Welcome to KZrider !
Bill/KZQ

maybe you can educate us some. the 1300 is kind of rare on here. at partzilla there are two oil pan diagrams for the 1979 kz1300-A1: in one diagram there are 2 drain plugs side by side facing forward; in the other diagram there's only 1 which also faces forward. plus in the crankcase diagram there's a 3rd oil drain plug, but facing downward. so. which drain plugs?  ... ps: is 17mm the actual size or is that the wrench size. guessing the latter. thanks.

Ebay listing below has lots of oil pan images:

ebay.us/m/OplZPm

Frankly, I don't get it either... 
🙃

        ThankYou for the responses. I located the drain plug with a socket wrench 17mm between the first and second exhaust tube on the clutch, stator side of the engine case, it faces forward and canted downward a little bit. 
I went on a ebay search for kz1300 engine and posted sone pics from the site.
i also found similar photos in the KZ1300 manual on page 91.
See the pics, I believe this when drained yields about 5 oz. The best I can figure is it drains one or both the stator and clutch compartments?
When I did the oil change the bike was sitting for a couple of months. I did not warm it up or start it up, I figured it was drained about as good as it gets.