However I discovered two things;
1) The defective units might be OK after all; after a clean and lube job they are presently doing a fine impersonation of working STIs. I can only hope that this continues....
2) There are several places on t'interweb where there are various write-ups on STI repair including photos already.
6400 STIs;
http://translate.google.co.uk/translate?hl=en&sl=zh-TW&u=http://tw.myblog.yahoo.com/jimmy63723/article%3Fmid%3D9932&prev=/search%3Fq%3Dshimano%2B6400%2Bsti%2Brepairs%2Bjimmy%26hl%3Den%26tbo%3Dd&sa=X&ei=qu8HUZL6LO2W0QXCsIGwCA&ved=0CE8Q7gEwBg
about a dozen or more good quality close-ups of RH 6400 internals.
http://www.flickr.com/photos/troysmith80/8394575672/in/photostream/
same photos in a thread plus other info here;
http://www.bikeforums.net/showthread.php/610670-8spd-Ultegra-STI-shifter-(original-style)-rebuild-guide/page2
Other STIs including later ultegras;
http://www.norvil.net/pedal/service/shimanosti/index.php
Sheldon Brown (plus other links)
http://sheldonbrown.com/sti-repair.html
Sora RH
https://sites.google.com/site/reukpower/misc/servicing-shimano-sora-sti-fix
This link suggests acupunture...


http://citizenrider.blogspot.co.uk/2009/07/how-to-repair-sti.html
If there is sufficient interest, I can post a few details of how these units work; understanding what should click and when, and the nature of the parts in question, can make the difference between (say) freeing off a sticky unit, and wasting hours on one where there is a broken part inside.
cheers