Back in the 90s - before after market idlers existed, and Subaru wanted $90 per idler - I converted the brackets on some old tensioners to use replaceable standard bearings. The idler with the teeth is already a standard bearing. I buy known name brand bearings with contact seals, and replace only the bearings.
The tensioners have a swaged post with a standard size bearing [looks like] friction / spin welded onto it. I turned bar stock into posts for standard bearings, and swaged them onto the flat brackets.