Not for any of my MBs, but I bought a remanufactured gearbox for my VW some years ago (the new OEM units were also unavailable).
Used ones are probably okay when tested, but the remanufactured units get the deteriorated parts replaced (i.e., seals).
I only consider the purchase of used parts when their function is static (body panels, trim, chassis parts, etc.). Otherwise, if a new part is unavailable (or cost prohibitive), I will always opt for the "freshened" or remanufactured part...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car