I have a '91 300SE.
Am I the only poor guy with no torque converter drain (trust me, it's original tranny and the drain is non-existant).
I drain out about 2.5 quarts when I remove the pan and do the filter change; and maybe 2 whole quarts when I just pull the pan plug.
Consequently, I try to do it often; but I sure wish there was a way to get
more fresh fluid in.
But, so far so good - 175k and no issues. I use Valvoline Dex III.

DG