Here is a parts diagram for your bike, they can be found at cmsnl.com.
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The sprocket is held on with two bolts (#16) and the plate (#10). Slide the sprocket onto the shaft, followed by the plate. The plate won't initially line up with the sprocket bolt holes. It must be rotated slightly after it has been slid onto the shaft far enough, essentially locking the sprocket in place. A small amount of play is normal once the sprocket has been bolted on. It helps to put the bike in gear when tightening the bolts, as this prevents the sprocket from turning as you attempt to do so.
Also, if you are replacing the front sprocket, I would suggest to replace the rear sprocket and the chain as well if they are worn. If one of these items is worn or damaged, it will wear out the other parts prematurely (I learned this lesson the hard/expensive way).
As far as the chain oiler is concerned, yes engine oil is deposited on the chain by means of a hole in the countershaft, and it usually cannot be turned "off" without some modification. I would advise doing this, as it will continue to create a mess until the oiler is disabled. Check out this thread for help with the oiler.
http://forums.sohc4.net/index.php?topic=10817.msg101695#msg101695