Thanks to you guys for the suggestions on roller replacements. I ended out getting 4 bathtub door rollers. Thet were $4 and the right size. Shower door rollers had plastic on the center shaft and I figured the heat would damage the plastic.  I drilled out the threads and used a wood screw to attach them. I made sure the screw threads ended and the aluminum wheel had a smooth surface to roll around.

 I tried it out this morning and it seems to do the job OK. The real test will be how they do after continued use. 

To be continued

Inline skate wheels work great.  You can buy used skates at Goodwill really cheap and just rob the wheels off of them.  They have center bearings.