you have to have 17 digits and you can decode it here : Yamaha VIN Decoder @ Motoverse.com
i just checked it and it didn't register, recheck you digits ...
when we both read about the oil change and the bleeder screw, it was for an oil change without changing the filter. if you change the filter too, you shouldn't have to do this.
the plug at the bottom of diff is to drain, and the middle plug is inspection and fill hole. just fill gear oil to the top of the threads, as far as opening a bleeder valve, i have never done that, but i just saw that in my manual too.
is it like a heavy knock like a crank bearing or sorta a ping like a valve? can you feel the engine and kind of tell if it's top or bottom end?
the jumping forward and backwards might be a belt ...
there are a few polaris guys on here that might have a better idea, wylde1 and polarisrich i know off hand have them and do lots of work on their own ... maybe send them a message to look at the thread you posted ...