Transmission fluid.
Fix the cause, or keep adding fluid.
Mopar ATF+3
The better question is what is leaking transmission fluid?
please be more specific is it leaking engine oil, coolant, transmission oil, brake fluid, or power steering fluid where is it leaking from ?
fluid is a lubricant of transmission
If it is leaking trans fluid into the coolant it can cause overheating.
The output shaft seal has failed and transmission fluid is leaking by, and that would explain the transmission fluid appearing there.
Buy a new transmission oil pan gasket before your transmission blows from leaking liquid.
Obviously a seal has failed.
Because your transmission has a seal that is leaking.
Determine the origination of leak and repair Could be transmission cooler line, seal, etc.