Tranny oil change..

Is there a sticky or a link on a how to?
I have 71,000 miles since my last change..

The "how to" has been discussed several times. We probably should make one a sticky. Are you doing a drain/fill, or a full flush? They are detailed here, but I don't remember where, short of searching for it. I've written about it several times, including a step-by-step for a full flush.

Probably a drain and fill..my trans has about 200,000 miles on it, it’s a rebuilt..

I just typed up a lengthy post for service an ALLISON tranny, then realized, you have a ZF. Just drain and fill. In the future, perhaps a bit sooner. 71K is a bit long. Pay attention to what comes out of it, and on the drain plug. Use a quality synthetic fluid (Mobil 1, Amsoil, Redline, Royal Purple, etc.).

Thanks....

Did the change, dropped the pan..there was a dusting of metal on both magnets barely noticeable, and the oil was red like it was new..

That sounds good. A little "dusting" is normal and expected, especially for the miles. Chunks or shavings would not be good.