My 1987 300E has been MUCH more reliable and about 1/3 the maintenance and repair parts/labor costs of our 1988 Acura Legend coupe. (I compared my records on each). It has been about the same as our 1984 Celica GTS in reliability and expense - extremely good.
The 'trick' with the car is that all - absolutely all - of the maintenance on the car has to be done by the book and on time. If not, you are generating extra repair costs (example - skip changing the coolant or use a cheap coolant, and you will wind up buying at least a water pump!) These cars don't seem to tolerate neglected maintenance. (but the Acura had premium and early maintenance as well, yet still ate us alive on repair costs, as well as having repair costs you won't find on the 300E - front CV boots/joints every 20-40k miles and rapid front brake and tire wear from crappy weight distribution.)
I haven't found anything yet that needed repair on the 300E more frequently or more expensively than that Acura, which had smelly AC by 50 k miles ('all cars are that way' - dealer), a failed AC by 80k miles ( 'you used it too much' - dealer) and a valve job by 100k miles (an exchange engine from Japan was less expensive than the lowest quote).
Point is, any car has maintenance issues, and even for the same model, some will be more reliable than others. Check the owners records - the more fussy they were on record keeping, then the better they were probably caring for their car. To me, missed records = missed maintenance = pending repairs.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E