R129 SL500 is a good choice...
Very good choice. May not have some modern amenities like Bluetooth for car phone. The soft top may need to be replaced. But overall the R129 SL500 from a later year (like 2000, 2001, 2002) would be a great choice. Reliable suspension (avoid the air suspension, get the metal coil suspension). The 500 engine is the M113 engine that I mentioned previously. Reliable gearbox, 5 speed. It is a car approaching 20 years old though; so I wouldn't call it reliable compared to a newer car.
And if you're considering a R129 SL500; keep in mind the R230 SL350 only with the AIRMATIC suspension (avoid the ABC suspension at all costs). The R230 SL350 will be more modern and have some modern amenities you may appreciate. But other than that; the R129 SL500 is a very nice car!