I have an 88. In the 5+ years, I've owned it (from 41,000 to now 91,000), I have had to do the following.
Before purchase in 1991. Head gasket replaced. Seller & I split the cost.Very
small leak rear left side of head.
Since then:
45,000 mi. injectors (routine & scheduled)
56,000 mi valve guide seals. (Steve is right on this one)
62,500 mi. flex coupling replaced.
75,000 mi. odo quit. & had replaced.

I have a little hitch in the idle. My dealer switched out a distributor from a yard 190E about 3 years. Problem still there. No better or worse. Still have the same distributor and same little hitch.

NO AC problems. Yet. Still original R12.

Thursday I will replace my original resonator and mufler. The res. has a hole dead center and it's starting to get more than a little growl.

I'm like most others here. I love the coupe.
Every time I see a Cabriolet, I get a little jealous. Then I slide the roof back, drop all 4 windows and think about all the convertible top issues I DON'T have with the D windows.

Go on over the the Open Discussion forum and check out the 300CE owners roll call.

Good luck with the car.