On Thu, 23 Feb 2012 14:03:27 -0700, chaniarts
wrote:

the problem is that the external threads that connect the nut and cover
most probably have mineral deposits, and there's no way to get vinegar
into the inside of the cover, so the cover won't rotate.

there are no trim plates or clips of any kind.

see part # 59425 in
http://www.kohlerserviceparts.kohler.com/ServicePartsPage.aspx?DocumentID=6b98dfbc1de946ad8 71337c4bda3bd3d&ModelID=7e26edaf142d4ddfb180746107 cfb600

it's the middle part explosion of the 3 on this page.

Try this: Use plumber's putty, rolling out a "rope" ( half inch thick
or better) then surround the part. Pour vinegar into the "pool",
allowing it to soak over night -- try again.

The putty will hold the acid (white vinegar).