We had a thread about this awhile ago. It seems that no one makes a perfect fit for these cars. I buy had to modify mine to get it to fit on and stay put.(I bought mine from NAPA too)
Might do a search here and see what all we decided.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)