Hi. I have 1990 300E 184,000ml
my mechanic recharged ac system with dye to find source of freon leak. system leaked out but he cant find leak anywhere. there are few tiny spots on expansion valve he says they are so tiny that it is impossible to leak all freon out through them in a year. my system leaked out in a month. are there any common sources for freon leak in 300E?
Thank you

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod