Like everyone else says, there should be two small bolts in the holes. Top one you add the chain case fluid, and the bottom is how you check it. Here's Polaris' parts thing if you want to varrify it's what your chaincase cover looks like:
You may want to pop the cover and just replace the chaincase fluid, since it sounds like it hasn't been done in a while. Polaris only sells synthetic chaincase fluid now, and I am not sure if you would want to mix the old conventional fluid with the new synthetic. I believe there is no drain on the chaincase on that year of machine. You just have to pop the cover and clean up the mess with rags.
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