This is what I found when I opened up my Borg warner 66. It was always late with the shift, every gear had a bump and the cable was zo bad the 'D' was where the '1' should be.

What's your opinion on this? Put it back and flush it?

 

Good heavens.

I have seen worse, but only just.

I would clean up that muck, and replace the filter, not forgetting the 2 gaskets on the spacer block, and refit that pan.

Refill with clean fluid, drive it for no more than 50kms, drop that fluid via the dipstick tube nut, then refill, driva again, and so on, until what comes out is the same (or very close) colour as what is going in.

I would not flush it with one of those machines, they can reek havoc with too much fresh fluid "shocking" the system.

If after 8 of those drop and refill processes, and based on the transmissions performance, I would drop the pan, clean it again if the trans is working OK, BUT, if its not working right the valve body will be gunked up, and need human intervention.

One I had needed the valve body stripping for cleaning to get it working right. The 65/66 valve body is a simple thing for the DIY to strip and clean. Just take GOOD photos of where the pipes fit BEFORE removing them, coz your memory simply is NOT that good.

 

Absolutely!!!! Pictures are a must.