I am surprised no one has commented on the practice of cleaning a clock without dismantling it, it is not a very good way to do it in one piece in my opinion.
It is generally the springs that get gummed up inside the barrels, and there is no way dunking it in a tank of anything will clean it properly, the spring must be removed to do the job right.
I have done plenty myself so speak from experience, I also design ultrasonic tanks for a living.
A general mild solution to use for cleaning the dismantled parts of a clock would be "Micro 90", I have also used an ammonia rich solution of "Horolene" or similar with good results in the past, do not expect the parts to come out polished and shiny, they will just come out as clean brass or steel. Also if you leave brass in too long, it comes out pink after the ammonia tries to leach out the zinc from the brass, dont ask me how I found out !
Most decent quality tanks will have heating built in, so when the parts come out they will be hot and they should flash dry fairly quickly. However a complete clock will not do this, it will retain moisture in all the places where it gets trapped, particularly the spring barrels.
Avoid using any ammonia based solutions on aluminium parts such as carburetors etc, that is unless you want to end up with a black one, dont ask me how I found that out either !
Phil