Plywood cut too wide for meatl roof ridge vent

The plywood opening is cut too wide at the peak of my roof. When a hard rain is wind-driven sideways, water is blown into the opening. A large windy storm caused our ceiling drywall to soak through and a small portion of it came down. Water has not entered during normal rains, even when heavy. My hubby wants to use minimally expanding foam sealant to close up a lot of the opening, but hopefully still leave a much smaller opening. Does this idea have any merit? My other thought is to contact the manufacturer and see if there is a wider ridge cap. But then the existing ridge cap would have to be pulled off? Can you monkey with metal roofing to that extent? Even if rain rarely enters, it will surely enter again. Suggestions?