Change ATF in a NON-quattro Audi 90 CS 1993 ?

I've heard that your can change automatic transmission fluid in a 1993 Audi 90 CS (Non-Quattro) but you can't in a Quatrro of the same year/
I am having transmission problems in my 1993 audi 90cs non-quattro and was wondering
A) Can it be replaced? B) Do I have to use the rediculously expensive ATF from Audi, or can my mechanic do it with today's (its 15yrs advancement in technology) ATF?
The ATF has never been changed to my knowledge. 166,000+ miles
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