There are other threads on this topic, but most will agree that the R129 series is pretty reliable.
Very little in terms of actual parts failures, which is good, since said parts are exorbitantly priced!
Most likely anomalies to crop up would be components in the complex electro-hydraulic top operation. Even those are uncommon issues.
Keeping the rear glass in good shape (why such a high-priced vehicle has a plastic window is beyond me) is paramount. Once damaged or faded, replacements usually entail refitting the rear area of the top, which varies from $340 DIY to upwards of $1200 for a pro install.
I've had my 95 since 2000 and except for accidentally cracking the gauge cluster glass ($273), I'm out a few dollars for burnt out dash bulbs ($12) and a broken console latch ($6).
Oh yeah, battery replacement last year ($120)...went to Interstate as the OEM version went for over $300 at the dealership!
Otherwise, periodic fluid changes is all I've done...I will contend that it's a fair-weather vehicle, so I put about 2500 miles per year cruising....