Considering 2002 that once leaked

My DH and I have been looking at used TMs. We came across a deal locally for a 2002 3124. When the first owners sold it to the current owner, it had a leak in the roof. The current owner recaulked the center seam of the front slide of the roof. Afterward, he removed the vent frames in the living area near where the leak had come in. The wood that these frames were screwed into was dark brown or black. He assumed it was mold and sprayed it with a fungicide. In the two years he has had it, it has not leaked since. He wasn't concerned about other wood because he believes it to have an aluminum and polysterene ceiling and walls. My husband is a handy DIY type of guy. Do you all think he can remove these vent frames and replace the wood (which may be darkened by wood rot or maybe its mold)? Or do you think there is other wood in the frame of this 2002 that is also compromised? Would mold grow anywhere else in the ceiling, such as on the polysterene, etc? Any advice would be helpful as we have a teenage son with allergies and we want to proceed carefully. Thanks!