I understand your concern for the 55/56 technology.

I never experienced a problem with the leveling system more than an occasional blown fuse, but I recall others that did. I suspect they, or their mechanics did not understand the system. It is well documented in the service manual. In most cases, the owners forgot to disable it before jacking the car to change a tire. Many mechanics were quick to jump into the leveling mechainism when it was usually only a blown fuse in a hard to find location.

The transmissions were great until they needed servicing. The torque converter contained a clutch that connected the engine directly to the tail shaft for an amazing cruising efficiency. There was something about the front pump and pressure to this torque converter clutch that only an experienced mechanic could get right. There are still experienced transmission rebuilders available through ads in Hemmings, etc.

Their engines were bullet-proof other than a failing harminic balancer. (Sounds like a recent Mercedes, no?) ...and there are lots of spare parts available.

Other than these items, there are no further quirky technologies involved.
Brakes are Bendix, Electrical items are Delco and Autilite.

Oh, and the 56 Caribbean convertible had reversible leather seat cushions. Meaning, when the top side became worn or soiled, you could simply flip them over and have new seats...

Good luck in your search. They were all grand cars in that era!

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)