Since posting before in this thread about using a vacuum-type RCM, I read the Merrill site more carefully and have been thinking about it. Perhaps I wrote too soon...
He says that the speed of the air rushing into the vacuum dries some of grime-laden water out, before it can be fully sucked up, leaving residue on the surface. I'm not sure how true this is, but it might be. Certainly sluicing a powered stream of water over something will usually get it cleaner than wetting, scrubbing and vacuuming. Think of a larger scale, such as a floor, and it becomes obvious. Ive had a wet/dry vacuum for years, and while it does a great job of cleaning a floor, blasting the floor with a stream from a pressure hose or even a garden hose with a nozzle could get it even cleaner -markedly so! So maybe the same thing is true on the miniature scale of a record's surface. Then again, repetition with the vacuum will do as well, and on vinyl I usually do a second cycle with distilled water. Vinyl isn't as absorbent as floor tile, nor is the dirt as well ground in. Without careful A/B testing and microscopic examination. I can't be sure, but I think he may be right.
The other question mark to consider is how good his cleaning solution is, and the fact that he advises spraying it on, and LEAVING IT TO SOAK for a while, before rinsing it off. How many of us let the cleaning solution sit on our LPs on the RCM while we go make and eat a sandwich. before coming back to vacuum it off? I sure don't. That might make quite a difference.
As for the steam cleaning some are recommending, it might well serve a similar function as letting the solution soak. Steam loosens and lifts up gunk much better than cool water... just think about how they clean car engines. The only worry I would have is the potential for the steam to perhaps affect the vinyl. Need to check on the melting point of vinyl, and how much it softens at lower temperatures. Just leaving an LP in direct sunlight can cause it to warp, so what might too much steam at over 200 degrees F do to it... or to the fine details of the grooves? Even if the heat isn't sufficient to cause noticeable warp in the record as a whole, could it cause any micro-deformation of the groove contours? It may be fine, but I'm not comfortable with the idea, without some checking and/or experimentation.
So maybe there are improvements to be made. Maybe this GEM system is better in some ways, besides being cheaper.
Perhaps the ideal solution (no pun intended) is a combined approach: soak (or possibly steam) well first with the best cleaning solution, then rinse off with that sink device, then follow with a distilled-water rinse (perhaps repeated) with the RCM. A little more time-consuming, but there sure wouldn't be much left behind on the record. Or use a distilled (or reverse-osmosis filtered) water supply with the GEM cleaner. I still like the final step to be the vacuum cleaner, to ensure a surface that is not only clean, but dry, too.
Hhhhmmm, then again, a hint of water might function as a lubricant, and it might help dissipate the frictional heat that is generated where the stylus meets the vinyl. I remember preferring the sound of slightly damp records, as a teenager. Perhaps a final stage of misting the record is a good idea? Or perhaps we should keep our LPs in giant humidors, like one does fine cigars?
As for the other complaint that the RCM involves physical contact with the record, this is, indeed, a drawback. It is important to keep the felt-like stuff at the edges of the air slot as clean as possible. This requres having at least two vacuum heads, and changing heads between the initial cleaning and the final (distilled rinse) cleaning.
Ideally, one might make an all-metal precision-instrument grade machine that would clamp the record securely enough, then hold the head just a fraction of a millimeter over the record surface.
I JUST FIGURED IT OUT! Just as I was typing that last sentence, a new design concept popped into my head that combines the best of all these approaches (except cost... no way could it be built as cheaply as the GEM). Now I have to go write it down (sketch it) before I forget it, and then decide whether to try to build one and perhaps patent it, or throw it out here for the world to have for free... Later!
Check this out:
.. and it has a high WAF :yes: 
