I knew a fellow audiophile back in the 90’s who had custom stands for his spica TC50’s. He had the 5” diameter steel post filled with transmission fluid and welded shut with the top plate. The stand was very heavy and inert.
turns out he was way ahead of his time in vibration management.
IMO that sounds like a horrible idea. Over time, sitting, ageing, transmission fluid's viscosity will change and the fluid will break down affecting damping. Not to mention, the slightest amount of moisture will rust the steel posts.