Water pump manifold
Not sure if yours is cracked or warped or another issue, most probably just replace the pump. The number to reference is89018039. Its discontinued, so finding them new will be more difficult. Here is one. Good luck.
https://www.ebay.com/itm/GM-LS4-WATE...75.c1#viTabs_0
https://www.ebay.com/itm/GM-LS4-WATE...75.c1#viTabs_0


