A properly converted system will have a label on the radiator frame alerting subsequent AC service providers of what exactly was done. Otherwise the telltales are adapters over the original high side and low side fittings. One is along a line between the brake master cylinder and ABS unit, the other is inboard of the left headlight visible when the hood is up.

You have to know what your looking for to tell if adapters are in place. After seeing a few you will be able to distinguish the marginally different size of the fittings.

These cars are closing in on 20 years of service so it's a rare car that won't need work with some frequency. If you find the right car, problems will occur once and not for another 100K miles. If you find the perfect car, most of these things will have just been serviced and you're free and clear for a long time to come. There are high $$ items like the front suspension, transmission and ACC, moderate $$ items like brakes and shocks, and the nickel and dime stuff like glow plugs, windows and door locks.

In my case, there's always something on the horizon. Shocks and brakes were just done but one of the front suspension bushings creaks. I replaced the head because of cracks and now there's the beginings of play in the turbo shaft. You can find $10,000 worth of stuff to make these cars absolutely perfect but be happy to find one that allows you to defer or tackle on your terms the major items.

Sixto
95 S420
87 300SDL
83 300SD