Use global variable in dialog's ControlCustomScript

Hi! I have used Dialog Designer to create a dialog with radio buttons and worked out fine. I have successfully managed to handle radiobuttons selections. However, I have the following problem: when I switch between pages my radiobutton selection disappears. So I want to somehow store the selected value in the outside script (I used a global variable like this Var /GLOBAL MAIN_SELECTION and store the value selected in each of the onClick callbacks for each radiobutton) and then use this value when dialog is recreated (defined in CreateFunctionCustomScript). 

The script I added was the following

MessageBox MB_OK|MB_ICONEXCLAMATION "Selection $(MAIN_SELECTION)" /SD IDOK
 
${If} $MAIN_SELECTION == "1"
    MessageBox MB_OK|MB_ICONEXCLAMATION "Select radio 1" /SD IDOK
    ${NSD_Check} $hCtl_MainPage_RadioButton1
${Endif}
 
${If} $MAIN_SELECTION == "2"
    MessageBox MB_OK|MB_ICONEXCLAMATION "Select radio 2" /SD IDOK     
    ${NSD_Check} $hCtl_MainPage_RadioButton2
${Endif}
 
${If} $MAIN_SELECTION == "3"
    MessageBox MB_OK|MB_ICONEXCLAMATION "Select radio 3" /SD IDOK
    ${NSD_Check} $hCtl_MainPage_RadioButton3
${Endif}
 
${If} $MAIN_SELECTION == "4"
    MessageBox MB_OK|MB_ICONEXCLAMATION "Select radio 4" /SD IDOK
    ${NSD_Check} $hCtl_MainPage_RadioButton4
${Endif}

But it doesn't work. My question is.
1) How can I restore the selected radiobutton when going back and forth between pages (back in my case)?
2) Is it possible and how to communicate some variables between main script and scripts generated by Dialog Designer?
 
Looking forward to any tip!
Thanks in advance.