Apparently at some point they stopped using screw-in bulkheads. The no longer have the 4 holes in the face, so they can no longer be tightened that way (not sure if they have threads or not). Now every source says end seals not replaceable, must replace entire rack. 
Andcal, you should be aware that this thread is a year old, even its last entry from July. By this time I’m sure the OP has long-since moved on.