I purchased a Fastrak SD and have removed blades for sharpening. After removing the bolts, metal cup washers, and blades, I was surprised to see a paper-thin black plastic washer between the metal cup washer and the underdeck. Two of the three film-like washers were ripped. They don't seem necessary (a washer for a washer), but I really don't know and they aren't mentioned in the owner/part manual. Any ideas on what the real name for this type of washer, reasons to replace, and anywhere online to order this? The dealer is an hour away and I can call him next week, but it would be good to know what the part is called and get different opinions.