This replacement part will come in two pieces, instead of 1.  The plastic piece, and a metal shaft that goes through the middle.  It's stronger, with lots of reinforcement inside.  Color may vary between Gray, White, or Black.

These are sold each, but the price is less for buying more.  If you buy 2 they are $21.95 each, if you buy 4 they are $16.95 each.  And shipping is included.  

Here's a couple of options for anyone who needs either the roller, or the insert, and doesn't want to buy them.

One option is to made something that will work.  Look at one of the pictures below.  It's a piece of hardwood that someone cut, and trimmed the edges of, and drilled a hole, then put a hollow metal shaft inside the wooden piece to make it work.   

For the Insert, remove the old insert, and use a wood filler to fill the hole where the insert goes, sand it down, and then drill a hole in the center to the size of the oblong roller shaft.  I hope that helps you.

Approximate Dimensions

2 1/8" Long Plastic Roller Portion, 1 1/2"  From Metal Shaft to top of Plastic Roller, 11/16" wide, 1/4" Shaft