MB doesn't recommend using anything in A/C system to find leaks! Use of dye will void warranty on their replacement A/C parts(rebuilt compressor) if they inspect them. But in most cases it doesn't seam to hurt the system. Most good shops have electronic leak detectors that will find any leak that dye will show up on, but it takes more diagnostic time.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V