Evaporator replacement is about 20 hrs. book if I remember correctly. Depending on where you live, that could be $1000 - $1500 just for the labor!
I wouldn't go there until it was first confirmed that nothing else was wrong. Sounds like the leak is under the hood. Isn' t that where you've seen dye?
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.