Inspired by this forum, i went ahead and got me an ultrasound cleaner!
I had a couple of atomizers for generic dse901's, that are producing next to no smoke.
Yesterday, i popped the first atomizer in the ultrasound, cleaning it with tap water (expecting it to die a painful death by drowning!). After six minutes worth of ultrasound, i did see a fair amount of oily stuff leave the atomizer, but no black crud/buildup.
After blowing it dry and priming it, i put a battery on it along with a cartridge, and hey presto: NO CHANGE :-(
However, after fiddling a bit, i did get a bit of smoke. 3 drops into the atomizer: more smoke for a short while. Last night i put in a fresh battery and cartridge, and it seemed to be coming back from the (almost dead). This morning, it's giving me a fairly decent amount of smoke, not like a new unit but definitely useable

I guess maybe i didn't let it dry long enough, and i had water in the steel wool, which in turn kept the e-liquid away from the heating coil.
The bottom line: Ultrasound cleaning may be a way to extend the life of a wimpy atomizer, but i'm not yet 100% convinced. More tests to follow....