Mine was dark due to driving in D3 for few weeks at 50 mph. One time was upset with this tank and went up to 60 mph on D3. The high rpm and the lock up clutch not being engaged (in D3) caused high temperature and burnt fluid after 10,000 miles.

If I were you I would change the fluid at an earlier interval and come to a standard for that car.

In line filter:
I took off my newly installed in-line filter out and decided to put it on the cold side (fluid coming out of the radiator). I used a 3/8” size filter and a 20” hose. After removing the filter, I drove around with patched up upper cooler hose but my clunky shift remained.

When I installed a new upper cooling hose the shifts became smoother like it was before installing the filter. The transmission did not like the fluid restriction.

How is your extra cooler coming? I will be very observant if there is any difference in gearshifts. Let me. I am not sure using stacked plate NPT fittings will cause less restriction/pressure drop to the fluid flow compare to 3/8” hose barb radiators.

Ronjon
'93 850 125k miles