The 280 M110 engine was and is a very dependable motor. I've been involved with putting 300k on two different models a 126 280SEL and a 280TE that our shop has used for 15 years (we just replaced it with a 91 300TE).
I definitely prefer the injected models. The US versions with carbs had problems when they were new (everybody was having problems in those days making carburated cars meet emissions standards). When I worked at the dealer we went through scores of modifications to the carbs various systems to try to improve matters. Things don't get better with wear.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician