I'll add my 2 cents and agree with my learned and more experienced colleagues above and recommend staying with R-12. As someone who has a W124 with a factory-installed R-134a system I am here to tell you it is marginal in really hot weather, especially in stop-and-go traffic. This is in a system designed for R-134a, so imagine what happens if you are trying to "convert" an R-12 system (but not replacing the condenser, etc.)

Bite the bullet, get a new evaporator, stay with R-12.

Incidentally, book time for evaporator replacement on a W124 is about 13 hours. (The higher figure in a post above is probably for the even-more difficult W140 chassis).

__________________
Steve
'93 400E