My 2005 Sportster had these metal plates in the seat cavity that are rivited to the plastic seat body.
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The OEM rivets are aluminum and the heads corroded completely off on half of them. It was a real pain to fish the plates out of the cavity. Once I got the plates out, I drilled out all the intact rivets and replaced them with 316 stainless steel rivets. Those plates should remain intact forever, now.
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