[s-cars] A8 rear caliper specifics

[Mike Fitton]

What A8 years/versions do we look for to do this swap?  The ETKA 
mentions a couple different suffixes.

I think the B5 S4 rear calipers were also aluminum.  Any chance they're 
also compatible?  I notice they start with 8D, while the A8's start with 
4D, so...probably not.

Anyone know of a good source for them?  All my usual suspects don't 
carry them.  There's a set on ebay for $180, but I'm not convinced 
they're authentic.

-Cheers!
Mike