using _Rreadk with a partial key - any examples?

Hi there,
 
I am accessing a logical file keyed over the first four fields.  however, I 
only know the first field of the key that I need to access.  This field is a 
unique seq number so should be sufficient to locate the correct record, and the 
documentation for _Rreadk states it can use a partial key, but I am not able to 
successfully retrieve a record unless I build the complete key (which I can do 
in test, but not reality).
Ideally there would be a logical keyed over just the unique seq number, but 
there isn't and I don't want to add one unless theres no other way.
 
Is there anyone out there who has used _Rreadk with a partial key successfully? 
 would you mind providing an example of how the key was built (compared to a 
complete key) and the _Rreadk params?
 
thanks to anyone who can help,
 
- Adam

                
---------------------------------
 ALL-NEW Yahoo! Messenger - all new features - even more fun!