[exim] Two level auto-reply

Folks,

Running Exim 4.54 on Solaris 8 sparc. I'm trying to set exim so that mail to one of a particular group of local users always
generates an auto-response. The local names all begin with c208 and to pick these up I have configured the following router and
transport -

vacation_always:
driver = accept
check_local_user
local_part_prefix = c208
transport = vacation_always
require_files = ${home}/vacation.txt
# carry on checking regardless of the outcome of this router...
unseen
no_expn

vacation_always:
  driver = autoreply
  user = ${local_part}
  once = ${home}/vacation-once
  once_repeat = 0s
  file = ${home}/vacation.txt
  log  = ${home}/vacation.log
  return_message = false
  text = "\
 ------                                                           ------\n\n\
 This message was automatically generated by email software\n\
 The delivery of your message has not been affected.\n\n\
 ------                                                           ------\n\n"
  to = ${sender_address}
  subject =  ${if def:h_Subject: {Autoreply: $h_Subject:} {Auto-response}}

However, the local_part_prefix setting does not seem to trap messages to those usernames and they fall through to the standard
auto-reply router that only generates responses at 5 day intervals. Can anyone see what is wrong with the above?

Thanks,

Clive McDowell

Information Services
The Queen's University of Belfast