Do you keep the proper amount of coolant in the system? You have to remember that when you have a cast block and aluminum intake or another other aluminum part that has water going through it you will develope electrolysis if the coolant mixture isn't correct. This translates into the aluminum eroding and a leak will develope. If it's not a case of electrolysis then it could be caused by over tightening of the fan belt which will cause the bearings to fail and then the seals will leak when that happens.