My old system before I had to sell it (Sitting on top of the Eurorack). Sadly I have never used an original 258 but the 258v by Mark Verbos is one of the most amazing oscillators I have ever heard. Outer space FM, amazing drones and bell sounds this oscillator does it all. And the great part there are two in one module. The best part is when you crossmodulate both oscillators. Mark even added a trimmed 1.2 volt/octave CV input.
From the Buchla historical homepage: "Two independent voltage-controlled oscillators, continuously tunable from 5 Hz to 20 kHz. Each has two processing inputs and a frequency modulation input. Waveshapes as well as frequency can be voltage controlled. Model 258 oscillators feature low sine wave harmonic content, negligible settling error, and high short and long-term stability, even with rapidly changing ambient temperatures."
This will be my next oscillator for sure as I miss it dearly.