Your best bet is to take this car to a indie benz shop and get an expert's opinion on what this car needs. I bought an 87 420 sel in the SF bay area where we have a mild climate so the body looked good. Heres what was wrong with the car :

lower Ball joints
upper control arms
rear sway bars
front and rear shocks
guide rods
idle arm bushings
engine mounts
steering wheel damper
shift linkage bushings
front brakes
L, R and center tie rods
new spark plugs
new fuel injectors
timing chain, tensioner and guide rods
A/C system recharged
antenna not working
replace original becker radio
drivers side door lock not working
new water pump
replace various bulbs
re-dye leather seats
one tire mismatched
O2 sensor
Im sure there is other things Im forgetting.

Most of these repairs are due to worn out parts.
My mechanic's estimate was over $8,000. to get the car road worthy.
I did it for about $ 2200 in parts and paid $2500 for the car.
Unless you see service records that show R/R of parts through the years, you can bet there is lots of work that needs to be done on the car.
And I doubt that this car gets 23mpg even on highway driving. I get 20 highway and about 15 city.