How can I configure a Brother MFC-8420?

[Bruce Korb]

Printer configuration file for CUPS v1.4.6

I cannot seem to get it to work.  This works for 1.4.4:

<Printer brothermfc8420>
Info Brother MFC-8420 BR-Script3
MakeModel Brother MFC-8420 BR-Script3
DeviceURI usb://Brother/MFC-8420
State Idle
StateTime 1286042213
Type 8392772
Filter application/vnd.cups-raw 0 -
Filter application/vnd.cups-command 0 commandtops
Filter application/vnd.cups-postscript 0 -
Accepting Yes
Shared Yes
JobSheets none none
QuotaPeriod 0
PageLimit 0
KLimit 0
OpPolicy default
ErrorPolicy stop-printer
</Printer>

and the required ppd file is identical.  CUPS is unable to see
the USB device:

# lsusb|fgrep 8420
Bus 001 Device 002: ID 04f9:0142 Brother Industries, Ltd MFC-8420

but the usb backend cannot see it (/usr/lib/cups/backend/usb).
Given that I bought this printer 3 years ago as one I had good
reason to believe I could use it for a number of years, I hate
to throw it away because support was pulled or forgo OS upgrades
because they disable my printer.  What can I do?