Sounds like you are in the same boat I am. The wifes 88'TE lost it's charge. Had it recharged, but it went down again in about 48 hrs. (compressor would not come on). Had both sniffer and dye tests done and isolated the evap. as the leak. 2k to have it replaced (w/vac elements).
I considered going with a Cryoseal type product as a temporary fix, but my leak is to large (will not hold vac.). You may want to consider this option if your leak is small. Have the system tested (must hold a vacuum at 25" for 5 min.)
I would do this job myself, however I do not have the time this month and my wife is baking (we live in SC).
My system is converted to r134 (previous owner) and I get 34 degrees at the vent with a full charge.