In my case, the rubber/glue was so disintegrated that the "tire" / wheel cover would not stay centered and kept leaving marks. So I just got rid of it. You could place a thin strip of duct tape or something else if you wanted a cover, but there's no real need for it.

I decided to photograph this after I had reassembled it. I would recommend you do this assembly before placing the scroll wheel back onto the logic board.

With the recess pointing to the left mouse button, line up one of the hubs and push the other side until both center hubs lock in place.

Then, place the haptic feedback arm in place by inserting it into the recess, and lining up the left of the two locking clips at the rear of the plastic housing and clipping it in place. Leave the right side unclipped at this point.

I found it easiest to insert the spring at this point.

Compress the spring so that it sits entirely underneath the arm. (See photos #2-3)

After a few tries, I was successful by compressing it with a paper clip, prepared as shown in the next step. But anything will do the job. The important thing is that it's small enough to allow the right side to click into place while the spring is compressed so the arm sits entirely above the spring.