MAC-11B vs MAC-11C

[Dave C.]

What's the difference between these ?
Are they interchangeable?
Which vehicles came with which?

Both have the same Audi part number.  I seem to remember hearing there is
no functional difference, but would like to confirm.

And BTW ...
I tried searching the archives for the answer.  I got lots of hits for this
frequently discussed topic, but almost all of the links do not work.
What's up with that?
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Dave C.