Well on this one I have a firm contradictory opinion based on industry standards and years of experience.
I have never met an idependent Airconditioning specialist (A/C only type business)that doesn't use flourescent dye. It has taken twenty years of competent use to finally get a few manufacturers to accept the technology. Untill MB puts its label on it they won't recommend it.
At a recent MACS (Mobile Air Conditioning Society) seminar the trainer gave a recent overview of current manufacturers positions on flourescent dye. There are currently a number that have approved its use (Not MB or any other European except maybe Volvo).
I would hate to point out that evaporator sales are improved by the use of electronic leak detectors. I have had about 20 electronic leak detectors. Never have I used one for longer than a year with any confidence. We currently have about four in our shop. We use them for first line diagnostics (big leaks) and for quality control on repairs, but I have never replaced an evaporator that wasn't diagnosed or confirmed with dye.
On BMWs the expansion valve is inside the evap case with the evaporator. Using manufacturer techniques there is no way to decide whether the evap or the expansion valve is the problem and thus both pieces are always replaced.
I have met many techs who have guaranteed good success rates by replacing everything involved. Dye testing is of no use in this diagnostic technique. We have used it for nearly twenty years and have used Tracerline products most of that time. We currently also use it for engine and transmission leaks. It allows you to see through the mess.
I actually think dye testing is a supreme example of the abilities that independent shops can offer to MB repair. It is one of many techniques that are developed for market situations and are consumer (performance)driven. The manufacturers have so many more considerations than efficient car repair. CSI is important and efficiency is often sacrificed where CSI could be risked.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician