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You can do it while its in the bike , you just need to make sure that all shavings are caught with a rag , i would place a shop rag under the basket all the way around , then (after removing all the plates) place another one on the inside of the basket , that way when you file the shavings get caught in the rag , file the grooves out but try to do so evenly at each tab , so do the same number of strokes if you can , try to make the strokes inwards so the majority of the shavings go to the inside of the basket onto the rag/shop towel , you are doing this with the bike lying on its side , what i would do afterwards is leave the cover off after wiping everything in/on the basket as best you can , and wipe everything down till you get no shavings on the shop towel (the Blue Shop Towels you can buy at most automotive parts suppliers) , replace all the plates then replace the cover and fill with a full quart of oil and you should be good for a while
As far as a replacement basket it all depends on what you can afford or what you want and how mechanically inclined you are , if you get a Aftermarket basket , you will need to remove the ring gear from your clutch and install it on the new basket with parts provided , if you don't want to do that or get that involved in it , you can get a OEM/stock basket and it will come with the gear , you can buy from your local supplier or dealer , or you can buy either aftermarket or OEM right here , Ken ships everywhere , and tries to be reasonable with shipping costs as best he can ...you will need a few specialty tools to remove everything ...... , i would recommend buying a Factory Honda Service Manual if you do not already have one , it will tell you everything you need to know about replacing the basket and tools needed to do the job as well as torque specs , etc .