These guys advertise a 'packing' for steering box seal. If you pull your seal out you will find its just a metal retaining ring filled with 'stuff'...I assume that is what this is...
http://www.ehfspares.com.au/index.asp?catID=747&listtype=27400608 PACKING STEERING BOX SEAL 48-HR
They don't seem to respond to e-mails so maybe phone them?
the one supplied with the RareSpares kit is a more modern replacement using metal/rubber combo...seems to work OK.
The web page noted above also shows Penrite steering box lube which I am reliably informed is the best stuff to fill your box with (so to speak)..
J