hamish is right. Antifreeze is POISON to the clutches in your automatic transmission. In fact the Allison transmission people make a big deal about not using the same funnel to put in ATF that you use to put in antifreeze. The tiniest trace of antifreeze, even the tiny amount from a well wiped off funnel can ruin an Allison automatic transmission.
It's very possible that the same holds true for other transmissions.
The glimmer of hope here is that the pressure in the transmission cooling lines is much higher than the pressure in the radiator. This may keep the antifreeze out of the automatic transmission.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in