My old edition of Handloading by the NRA lists a vinegar and salt solution of 2 tablespoons of salt to a quart of vinegar. Soaking for 15 to 20 minutes, shaking and stiring occasionally. Then rinse for 5 minutes under running water.
It is supposed to soften and wash away fouling, which can be wiped off if needed. Never tried it myself, but may work good in a vibrating case cleaner.
That article also lists a Frankfort Arsenal recipe of 5% citric acid solution for 5 to 10 minutes followed by a rinse in water, then a final rinse in soapy water. They said that they tested this and it did clean the cases, but did not leave them bright.
