I have a 1991 740 non-turbo sedan. My car is leaking transmission fluid rapidly; I go though a quart of ATF in like 50~75 miles (I've been very attentive keeping it topped off). It looks like the leak is coming from right behind the firewall. What could be the problem?

 

It could be a leaky tranny cooler line. There are two ~5/16" metal lines that run up the right side to the radiator. Sometimes they get chaffed at a hold-down bracket, or rust, and develop leaks. You should be able to spot the location of the leak at idle.

 

I've looked under the car when it idles and it looks like the puddle forms right behind the firewall. It's too cold to go underneath and actually look at the tranny.
Is this causing my car to overheat?
Is this something I could bring to a local shop and get fixed for ~$100 in a couple of hours or would waiting until Sunday when my normal mechanic can work on it for free?

 

I went to a shop and it is the cooler line. Thanks for your help.