1995 Dodge Caravan Sliding door on passenger side

1995 Dodge Caravan 6 cyl Front Wheel Drive Automatic

I have a 1995 Dodge Grand Caravan and the sliding door fell off today. I noticed the part where the bearings travel to allow the door to slide back and forth has broken(it's the middle set of bearings) it looks like I'll have to replace it or have it repaired. However we have a "pull your own part" place in town and I need to know the name of the assembly and is it hard to replace it yourself.

Many thanks
Mary Ann