[Dakota773]

I just replaced them last year on my 98 31 Open.  Dapagani's post is correct they are Delron plastic. I got a slab from a local plastics supplier, $120 or so for a 3"x1"x 24" bar that I machined myself. No real issues, except aligning some of the holes, but with a little tweaking, sandpaper and patience it all went in fine and works great now.  The originals had worn some and cracked, so using them as templates probably caused some of the alignment issues in the end.  Also, I was working with basement tools, if you have a drill press you'd be in good shape to cleanly align the pieces once they are cut on a table saw.  Only other issue was some of the bolt holes in the bottom of the seat didn't align. Same thing, a little patience and all fit eventually.