Water cooling block won’t come out

I bought an untested power Mac G5 yesterday to hopefully use the case for a modern rebuild. However when I opened it up the coolant had leaked all over the PSU and radiator. Even when I removed all 8 of the screws it won’t come off and just rocks around.

Have I missed a screw or something or has the coolant done more damage than I first thought?

Could it be that coolant has corroded the socket pins together?