I have a 1981 vanagon, California model, which means all the smog
equipment.  There is a relay called the speed limit switch, as shown on
page 24.14 of the Bently manual or called the OXS relay when looking at
the wiring diagram on page 97.12. The unit on my van is all corroded
inside. Can anyone explain the operation or function of this unit. It
has part number 071 906 069.  This is a good number as confirmed by the
local VW parts house, but they had no info on it's use. My van starts
ok, but will quit while flying down the freeway. Some times for only a
second but some times for up to 30 seconds before firing off again.  I
KEEP TO THE RIGHT ON THE FREEWAY!! I have been running a test box
monitoring the voltages associated with the double relay, but have found
no problems there.  Questions:

1. Is this speed limiting switch/oxs relay necessary.
2. How does it function? What does it do?
3. Where can I buy one at a reasonable price. So far I
    found it to be a dealer only item, highly priced.

Thanks in advance for any helpful input...Steve.