The 1.9's had head gasket problems under jack-rabbit driving conditions, such as long paper-route driving.
I went through at least 5 engines. Normally, they run slightly overcool... then you jack rabbit them, and they heat up nicely... then you chill for a minute, and they cool back down. Toasts the head gaskets quickly.
The engines were only $100, though... so I was still making a butt-load of money.
Great job on maintaining her for half a mil, man!