Convert a Field

Hello,
I have a CHAR(12) field in a table.  This field is a last 12 month field, so it provides 12 characters representing each of the past 12 month.  Problem is, the 12 characters in this field could be blank.  So when I go to export, it gets all messed up.  Is there a way to look into a field and convert any blanks into a value; say; x ?  

Field will look like this:
'1   12   1 1'
'         11 '
I want to see this:
'1xxx12xxx1x1'
'xxxxxxxxx11x'