I have a 650 seat, however it was reupholstered sometime along the way. The vinyl used has a funky pattern and the stitching is wrong. I'm being a little picky.
I've seen the cover kits on eBay, but I don't want to take the chance and ruin this one. Tempted to buy the XS1/2 seat from MikeXS. I found the 500 seat for cheap and was hoping to get lucky with a fit.