Offshoreonly.com - Gear oil reservoir split open

Hi everyone. I'm new here. Typed a long post earlier about my gear oil reservoir cracking open but I did something wrong and the post didn't go. Boat is 4 years old. Serviced religiously. 117 hours. 6.2L Mercruiser. Bravo 1. No leaking cap on the reservoir like I've read in hundreds of post. All is good 1 minute then alarm blaring the next minute. Open the hood and have gear oil everywhere. Pop off a cover to expose reservoir and it's split across the top and down the side. It's a square reservoir with black top and translucent white box. Cap has seal and red rubber nipple. Oil was at the full mark when we started. Oil is new and what the book calls for. I change it at the end of the year every year for the last four years. Trying to figure out a cause and have only one indecent at the end of last year. I was backing in the trailer and my wife is on the boat pulling up to load up. She had a prop strike hard bottom in Lake Travis. Pulled the boat out. Very slight bend on one blade of the stainless prop. Skeg has two small chunks missing directly behind the prop. Got home brushed it off. Changed oils and tucked away for the winter. This cracked reservoir happened our first trip out. Could the prop strike have caused gears to misalign and over heat the gear oil enough to pressurize and rupture the reservoir? Could I be lucky enough to have a bad reservoir and just replace it and change the oil? For the short time we ran it there was no vibration or odd sounds. Just got home and haven't pulled the drain plug yet.