Some noise from the front of 5-speeds is normal, what fluid are you using? In the US manual trans in any Mercedes is rare so finding any tech who has repaired these transmissions can be difficult. MB recommends a special ATF that only they sell. I use Redline syn. ATF in my racecar. Try changing the fluid & see what comes out(metal).

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. TECH
190E 2.3 ITS RACECAR