I highly doubt the shafts need replacing as they really don’t wear. I rebuilt mine and it was simple and inexpensive. Mine were dripping at the shaft before and are working great now.
You take out the upholstery piece that the speaker hole is in the arch and run a fish tape up toward the dash area. No need to try and access through the sub speaker or cup holder.
That is why it is smaller, it only has one vent. I just replaced both and upsized the front to a 16k and the aft to a 9k and had to add a second vent to it.