[BiturboS4] Dead turbo - it hurts !

[David]

That's it.
Yesterday, I have brought my car to the Audi workshop, because it had the
"thermal plate rattling". In the afternoon they called me to say that they
have found a damaged turbo. They want to sell me a "standard change" turbo
(it's common in France and Spain for expensive parts) which is a used turbo
serviced and guaranteed by Audi. It's supposed to be like new, but it's not,
and the price is "only" 1160 €. They told me also that they see no problem
in changing only one of them (I've always heard that turbos had to be
changed in pair in the S4).
I need your opinion, guys !
David.
S4 Avant Abt - 1999 - 37500 Km.