OK Kiddies, lets remember we're all playing silly buggers with cars and components that are the best part of 20 years old. When doing things like
flushing engines, corrosion is quite likely to to rear it's ugly head...
even if it has had had anti freeze at the correct levels for those 2 decades
it's not inconceivable that some of that alloy head has called it a day
and just let go. Not sure why one would decide to flush an engine but as me old Grandad used to say.......if ain't broke don't try to fix it.