If yes, what kind is best? A Halon or something else? Price, location to buy and place to mount (on the 126 in this case?)

Worth it to go and look for the OEM 126 one? Or just go to Pep Boys, Autozone or Napa?

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)