Realistically (all things considered), the car has been amazing. And there's something to be said about top tier comfort on 1200+ mile drives. We've taken this to the bay area several times (from Phoenix) and each time, you can put the heated seats on, turn on the massage seats, and then everybody can watch a movie (the front seats have LCD screens behind them; you can actually put on two different shows). With AIRMATIC, it's the ride quality is super comfortable too. AIRMATIC has gone bad and I've replaced those components myself; the rear air springs, the compressor, the valve block, and both front struts.
The engine is the only sad part. But it's also quite a happy part. When things are working (which has been most of the time over the past 5+ years; only had 3 incidents), it's incredibly fast (420 HP) and the fuel efficiency is not horrible. We've put over 70k miles on the car - so it definitely gets driven. We also got it for $27k - so even with the expensive repairs, we didn't lose as much as the original owner that plopped down $95k for the car
If you only have 4 cars in the stable, this is a pretty awesome luxury cruiser. And if you know ahead of time how expensive the repairs can get (it doesn't help that parts prices and labor has increased), it's somewhat reasonable. But I do love being able to service the other 3 myself (87 300D, 87 300SDL, 2006 Ford Ranger 5 speed w/ zero options).
Funny story - I can't remember if I shared here already. But this 2013 GL550 is the newest car we have. It has an electronic parking brake which I didn't know about at the time. I went to replace the rotors and pads myself. Front went perfectly. Got to the rears and somehow missed that the parking brake wasn't a drum brake. I couldn't get the caliper w/ the new pads back on and the piston wouldn't compress. I found out there was a service position that you need to set via the cluster. That made things better, but the piston wouldn't compress well.
Disclaimer: I only had a crappy C clamp at the time. Now I have the proper Hazet piston compressor
Since I couldn't compress the piston more with the tools I had, I thought it might work out like computer problems. Turn it off then back on again. I went to the cluster, turned off the service position for brakes and then figured I can turn it back on again. Well - without something for the piston to have stop against when turning it to off position, the piston kept twisting out until it flew off completely and brake fluid went everywhere. At this point, I clamped the soft brake line, hung the caliper off the control arm, and called MB roadside to have the shop fix my mistake

I've since learned the proper way to do it. But things are certainly different than the W124 and W126 era!
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