Exciter 570 Base gasket problem

so last year i purchased a 1987 yamaha exciter 570. the engine was rebuilt 200miles prior and it ran great. i did some basic repairs and bled the cooling system. a little while later it blew the base gasket and leaked coolant everywhere so i took it apart replaced all the gaskets and put it back together it ran great but now it has blown the base gasket again any ideas?

Exciter 570 Base gasket problem