1989 Cadillac El Dorado oil or transmission leak

Hello,

Ok, since it is between the Rad and Engine I would say it is a Transmission line Leaking. Take a good look at the fluid if it is Red/Pinkish then it is Transmission Fluid. Usually it's a steel line that has rusted through or is against something and rubbed through in either case the fix is to just cut through were the hole is and push a piece of rubber gas hose over the pipe and clamping. DIY Repair cost less than $10.

I didn't mention that the oil spill was more brownish than red, meaning possibly not tranny oil leak, is this possible given the location of the leak?

Ok, check your tranny fluid via the dipstick and check color, if fluid is old it could look brown.

It could be if you have a remote engine oil cooler, some people will add them if they do a lot of towing and will also add a addition transmission oil cooler, both are mounted on the front of the radiator and look like small radiators.