If this is for a W126, the local guy should be fine due to the relatively simple nature of this chassis' steering geometry. My flame suit is on, and I realize the *correct* answer is to always use the dealer, but I have had adequate results with the $40 guys. The tires on my W126 are wearing almost perfectly evenly.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280