Galvanized transmission oil coolers

I've got a new water cooler here, and I've got no use for it. Now I wonder if someone knows when and why Audi only installed coolers with tinned transmission oil coolers. See pictures. My replacement cooler has the number 441121251E
According to part film 06/1990, "E" has been converted into "G" (well then tinned?), which then resulted in 10/93 in J. According to the repair guide only coolers with G should be installed. Now I wonder 1. whether my replacement cooler is tinned or not, 2. why Audi changed that and 3. what happens if I mount a non-tinned cooler.
Since the supplier Länger&Reich was taken over by Modine in 1993, my replacement cooler must be at least 27 years old.
My friend could not help me even after direct inquiry at Audi.