That's REAL nice. LIke getting a brand new one almost. The last year of the W123 too. I wouldn't worry about getting another Becker radio, from that era, they are considered crap, not worth the bother.
Just drive it and enjoy it. Can understand why you are crowing, there is LOTS of interest in these, even more so when miles that low - and that is absurdly low for the year of the car. All the better that you know the history of the car.
You sound delighted with the new purchase, that is what really matters.
You could realistically expect to get another 400,000 miles about it if you take good care of it. Now that's really cool. I am really happy for you, you got a gem and you know it
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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)