Mr. Monk Meets His Dad - S5-E9
Plot hole: Monk's dad, Jack, drives an 18 wheeler. In the scene where Jack pulls over to the side of the mountain road so they can discuss specifics about the GPS, a brake line is shown breaking and spurting what I assume is meant to be brake fluid. The rig then rolls down the mountain. However, 18 wheelers don't have brake fluid since they don't have hydraulic brakes, they have air brakes. Even if the rig lost its brakes due to loss of air pressure, the brakes are spring loaded to lock up all the wheels in this case and prevent movement. That's how you set the parking brakes, by releasing the air pressure. In other words, if he has air, he can use his application brakes; if he's lost air, he has his parking brakes set. Rigs that lose their brakes going down steep grades do so due to extreme overheating, causing brake fade, an inability of the brake shoes to grab the brake drums. This wouldn't have happened while they were parked.
Mr. Monk and the Really, Really Dead Guy - S5-E15
Plot hole: In this episode, Monk doesn't know to open a cell phone to answer it, but in "Mr. Monk and the Kid", he used a cell phone with the ransom drop with no problems. (00:04:25 - 00:05:05)
Answer: The two men are trying to work out a secret deal between them without involving the union, which means the workers' interests aren't being represented and defeats the whole purpose of a union. The mayor would lose labor's support and Cusack's union troubles would just be starting.
Captain Defenestrator