Gnus and spam - bogofilter

[Richard Riley]

I have set up spam processing in gnus. I have set bogofilter in the
group parameters and specified bogofilter methods to be called for spam
articles when exiting a spam group. But no bogofilter headers  are being
added. 

I have added extra headers ^X-Spam-Status: Yes, and X-Bogosity
(instructions vary from help in google) and I have also set
spam-autodetect-recheck-messages to t.

I know the marking as spam is working as messages marked as spam/ham are
moved to the correct destination folders courtesy of group parameters.

I would be interested to hear from anyone with this working : what are
the necessary settings to get gnus exit processors to apply bogofilter
headers?