Within the past few months, someone on this list posted the correct generic
Bosch O2 sensor for the 2.1 L. engine as being a No. 21-156-8300.  I just
spent some time looking through Bosch's most recent O2 sensor book and
neither my ever accommodating VW parts specialist nor I could find any such
number listed as a legitimate Bosch number.  Would whoever originally posted
the above part number please let me know the origin of that number?

Rich