The SPLINE style head that DOC referenced above is also available at Pep Boys. The tool mfg is Lisle Corp. Part is named "12 point bit set". Part # 60750. Viewable at their WEB site:
Click on Special Tools -> Catalog -> Fastener
Lisle tools are widely distributed in the U. S. and Pep Boys is certainly not your only choice. Stahlwille, Hazet, Snap-On; Mac also carry this item.
In closing, the 12 point bit is also known as "triple-square" and "XZN". A sales rep at Baum Tools told me that MBs use TORX, XZN, RIBE in addition to traditional bolt/nut patterns.
1991 300-SEL - Model 126
M103 - SOHC
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