in response to a message on the Corvette Forum # 315184
.81 AC Evaporator install, 5 hours labor, tricks to installation

I would suggest a replacement rather than a repair of an AC evaporator, especially if it was any original of that age. The difficulty of splitting and removing the 2 piece inlet-outlet halves of the evaporator case and core are challenging to any mechanic. The five hour labor charge could actually be low. Should you undertake the task yourself, it will be lengthy and uncomfortable. Have any new core pressure tested before installation, as you will not wish to do this job twice. Note that the evaporator core is actually screwed into the inlet or left side of this 2 pieces case. Simply separating the inlet and outlet cases will not free the core. If replacing the evaporator core on 1963-1977 models use care not to kink or break off the small bleed line as they are all Aluminum.

Starting in 1968 on Corvettes, GM began using a specially designed stepped seal to improve the efficiency sealing the evaporator core to the evaporator case. The stepped seal is shown as item B in this illustration and read how others here have reproduced this part. This part has been discontinued by GM for eons, but has been re-manufactured exactly by the original GM supplier for me. If you read my Tech Tips, you will know what they look like and get stuck with a replacement. You can purchase this part separately, or in our 1968-1982 AC/Heater Seal Kits to rehab the inner and outer boxes and ductwork. My advise is to get our kit, even if you do not use the pieces for the inner boxes now, it will save you time later. Eventually when the heater core craps out you will already have those seals also. Saves shipping later also.