An independent quote me $1,000 (most of it labor) for the evaporator and a change to R134 at the same time. I am a DIY and have the manuals.I did it myself since I paid the local dealership a lot of money in the past for a lousy job arghhh! They will never see me again. So, I figured I could not do worse that they did and kept the R-12 (my preference) but, it is a LOT of work. My AC is working fine right now. I hope it does not change in the future. If you have a GOOD mechanic pay the money and get the "upgraded" evaporator or aftermarket with copper lines.
Good luck!
J.H.
86 300E