Earlier quoted context omitted.
If i use the regular ferrofluid it can last for quite long, however i dont like the effect of the fluid in that case, it has spikes and doesnt really look like a blob that i wanted to achieve. I have samples that are year old and work just fine so far.
Higher viscosity filler fluid and/or a ferro-binding compound to dampen the "springy" vibrations and ferro "spikes"? Btw: Comes off a labor of love and insanely-awesome attention to design and detail. Outstanding. Kickstarter/indiegogo/lockitron selfstarter page yet? :)
KS, maybe one day :)