Had it happen to me
My water pump did the same and started corroding the front of the block and foward motor mount. It still cooled though. I took the water pump off and took it apart and was going to replace the seal on the back side of the impeller. I noticed that the shaft was badly worn so I replaced the whole pump.The parts were expensive by themselves so I opted to by a new pump and it has been serving me well. The moral is if take the pump apart and find alot of worn out parts then just replace the pump , but if you can get away with it you could change the shaft seal, the cover seal and the pump to block seal and it will work. Also check the impeller for wear or flat marks on ends of the rubber tips. If worn you can be cheap and flip over the impeller or just replace that while your there. Hope this helps, John