I'd just run some Mobil 1 through it in a couple of short changes. If you see actual sludge built up on the bottom scrap it out.

I'm sure all ours look like that inside. When I did mine the fluid originaly came out pretty clear. I replaced it with M1 and after a year it was black. The last time I did it, it still looked pretty clean so, it will do the job.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200