My 96 did the same thing, but it probably had something to do with the mechanic who serviced the oil cooler. Took truck in to dealer with an oil cooler leak, picked it up, took gooseneck to get a load of drywall for a house and it started leaking coolant, drove right back to dealership. Mechanic comes out to parking lot with two gallons of coolant and starts giving me a song and dance and tells me it has a crack, right at the same spot everyone in this thread has. Funny, service manager never mentioned it. Later found out...
if you take the bolts out of the rear of the cooler before taking the front bolts out, the cooler will twist that front mount and crack it. I point this out in bold so people who have the factory stock cover on an OBS, and really any 7.3, may avoid this issue by removing the front bolts first, or at least loosen both and remove one of them so it can't torque the mount. I ended up building a new engine and put a new cover on it but I still have the old one in the shop. Used it to mock up lines for dual remote IPR setup I still havent installed
That truck was wrecked and engine is in a buddies truck and hasn't had any issues. However, I also related to him how to avoid the problem if he has to replace the cooler or service it. Had I known a SD cover would fit and solves this issue, I would have used that at the time.