Can someone please tell me how much transmission fluid I will need to do a flush on my 1989 300CE?

Also, what brand is recommended? Here is what the local store carries:

1. Mobil 1 $8.99 Canadian /quart


Not the Supersyn pictured below


2. Amsoil $11.99 Canadian /quart


3. Castrol ATF $3.99 Canadian /quart


Here is a site comparing Amsoil to Mobil 1:
http://www.bestsynthetic.com/atf.shtml

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz