Can say I never heard about the casting leaking. But the intake gaskets on just about all vortechs (3.1, 3.8, 4.8, 5.3, 5.7,liters) have had the problem of leaking coolant into the block and externally. From the one's I have saw it was always around the stud in the left rear of the intake.(driver side) but not limited to that area. Always a good ideal to change them out as long as you got the motor out. The 5.7 in my truck and my friends truck both went between 100,000 and 110,000 miles. The 3.8 in my nephews Pontiac went at 90,000 miles. I know of a few more too all right around 100,000 miles