Since you love the car and are familiar with it's history, I would vote you make the needed repairs.

The W124 300E sedan is a proven and durable design, and as long as yours hasn't suffered terminal rust, I'd be inclined to keep it. Of course you have asked on a forum dedicated to keeping them on the road, you can't expect too many answers suggesting a new Toyota Corolla.

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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)