My 48 in Craftsman Riding mower with a Kohler 25 hp engine locked up

48" craftsman Riding mower. I have a 48 ' Craftsman Riding mower. I have had the mower for 4 years with app 450 hrs on the 25 hp Courage engine. The last cut I did with it , I slowed it down to back up and the engine died! Locked up ! It was a hot day and I had about 2 or 3 hrs of running time on it that day. That's usual for my cutting my large lawn. Towed it back to my garage and still locked up. Had about 25 hrs running time on the oil and it was still full. I pulled the engine and dropped the crankcase bottom off and it looks perfect inside but the crank is locked up. The rods still move on their journals and the cylinders look fine for what I can see. I`m guessing the upper main is where the lock up is. I have not yet pulled the heads off and the pistons out. If in fact I can get the crank out , is it possible to recon the the upper main journal and recon the block opening for the crank journal? Hate to junk this engine ,but what caused the failure. Has anyone run into this problem. I did have a Sears tech look at it and he said he has had a few that did lock up , and said the customer used a breaker bar and a socket to try to break the seize up on it and it worked and ran! I tried but no success. Should I look at something else on it. The crank will not budge either way but there is slack in the rods so I`m pretty convinced the crank is seized. All info much appreciated. Russ