Rollers for a Pella sliding door from the late 90's

Hi. I'm looking for a set of replacement rollers for a Pella sliding glass door. It's from around 1999 as the home was completed in August 1999. It's oak interior and I believe aluminum clad on the outside. Is there a standard replacement roller or do I need to take the door off to get a picture of the roller. Also, are there 2 or just one?

Thanks
Dave