Sure seems like a lot of money to throw after a solution that isn't the problem. These Gen II W126's blow mid 40s on a 100+ day running 134a. I don't know what you think the parallel flow condenser is going to achieve since the pushbutton unit switches off the compressor when the evaporator coil reaches 38-41˚ (42-44˚ vent temp). The Gen 1 (Pre-'86) cars are a totally different story.

I'm just waiting for the OP to come back complaining that his $300 coil and $100+ worth of R12 didn't fix his problem.