Re: Can anyone identify this transmission part?
Actually, I had been thinking the same thing. I actually drained most of the fluid from the transmission before unbolting the pan. I've got a hand-pump, and I find the job is much easier & cleaner to suck out the fluid through the dipstick tube first. I believe there are machines that cycle the fluid & flush, and then the tech can fill the transmission with new juice.
The fluid must have been changed at some point in it's life - the pan didn't have 21 years worth of fine metal "dust" that typically sticks to the bottom. While the fluid was dirty & needed changing, it still had a red tinge to it (but it wasn't bright red like new fluid).
I suppose there is a possibility that the pan has been dropped in the past, filter changed, and the plug was just left there. Silly, but possible...
Logically speaking, the fluid probably has been changed - the transmission functions very well after 21 years. I don't think it'd be very solid if it were never changed.