STREAM::expression Not Replacing Multiple Expresions

Hello - Hope you can help me. I'm using STREAM in an iRule to replace internal server names with external ones using vars and also to change http to https. It works if I using either one of the elements by themselves, but if I put them together in a single STREAM expression, only the http replacement works.

Here is the iRule:

when CLIENT_ACCEPTED {
  set sINTERNAL_URL "internal.server"
  set sEXTERNAL_URL "external.com"
}

when HTTP_REQUEST { 
  STREAM::disable 
 } 

when HTTP_RESPONSE { 
  if { [HTTP::header Content-Type] starts_with "text/" }{ 
    STREAM::expression "@://${sINTERNAL_URL}@://${sEXTERNAL_URL}@ @http://@https://@" 
    STREAM::enable 
  } 
}

Any ideas?

Thanks