Seems odd that it would move like that if the star washer behind it was folded in properly to lock it in place. I've generally seen those with one of the arms on the washer folded up into one of the slots on the nut to help keep it from rotating under force. It's a bit of work to remove it all but does seem to help.
The rear typically will show wear faster than the front, it's aluminum in the rear .vs. the front which is probably steel. I have the same thing on my bike, I tore the shit out of my rear sprocket, but the front is relatively unharmed. Im sure im the cause of part of that, it could have been misaligned slightly, chain a bit too tight etc etc at times but point being, the aluminum will eat it faster than steel sprockets.
You may have aligned the rear perfectly, but every time you tighten your chain when doing maintenance, it can knock it out slightly, hitting a big pothole can do issues, even though it shouldn't, etc etc. Although obviously you want it perfect, a slight alignment abberation is not going to cause huge issues, it's not like the rear MUST be within 0.001 mm or some other crazy stuff like that, and unless you are torquing the piss out of it with your riding style, aka on a race track or something, you'll probably see more alignment issues in tire wear.
It IS good advice though to check things every 10k. I believe there already is some maintenance on the bike if it's yearly or what, to actually go over everything and give it a good eyeball. Common sense would say to do that anyways really. when doing the annual changing the gearbox oil / cooling fluid, just check all the nuts and bolts, look for wear, damage, misalignment or things that seem out of the normal. Every time I take the race bike out, the first day of the weekend romp, ill give it a good look over looking for problems, you don't want something letting loose at 140 MPH on you now do you? Besides, looking at things fresh in the morning, first day, you tend to have a keener eye than after riding all weekend, you are sore, you are tired, hands hurt, knees hurt, and you are thinking of how comfy a bed is going to feel after camping for 2 days
If you are doing your chain maintenance, that front sprocket guard can over time catch and hold a TON of nasty crud from grease and road dirt, so it doesn't hurt anyways to take it off, clean that huge wad of glop out, and look at the sprocket, spline etc etc.
Aaron
