Here is an affordable product to repair loose door checks. Toyota Prius Door Check Repair Kit (4 doors) Stay Strap Stopper Replace | eBay With some DIY, the old plastic spacers will be substituted with new graphite ones. It took 30' for each one door, including dismantling & placement.
I wanted to report that I did all 4 doors recently with this door check repair kit linked above and I am very happy, no more doors falling into me when parked on a slope and all 4 of them needed it on my 2008. It comes with shims to add behind the rubber blocks for more resistance or pinch against the door check arm, but I didn't need to use them. I can easily add the shims later as these parts wear down. The package comes from Russia so it takes a while to arrive and it stinks like chemicals so put it in the garage or outside. The smell is likely the graphite paint, couldn't tell if mine had dried out a little as it was like a paste, but it worked. Use just enough to paint a thin layer and let dry for a minute, then you should have enough left to add as needed later to the arm. Toyota used grease originally, but this comes with the graphite dry lube so I am sticking with that for now. Door panels have to come off so consider doing it with something else on the doors like adding new weather strip for the side mirrors on the outside, two screws one at the door latch handle and another at the armrest and the panel pulls straight off starting at the bottom corner to release all of the push fasteners. There are two spot welds on each door check assembly that need to be drilled out so you can open it up. I prefer to fix something than replace it, but you can replace these as an assembly if you prefer or don't have the ability to drill. I am not sure why these don't mount externally then anybody could replace them without having to remove the door panel, must be a safety strength thing to have them mounted behind the door metal. Here is a video of the same kit used on a Toyota truck, similar concept on a Prius:
