I have cleaned the PCBs on the Apple-1 computers that sold from Christies and Bonhams among others.

Since I am dealing with boards that are super valuable in the hundreds of thousands of dollars, I clean them so that I can inspect them under a "microscope" as part of the "bring-up" process.

To summarize my procedure...

1) I use MGChemicals flux remover on high spray and basically go to town on the board with the chips in.
2) I then rinse the board using 99.9% alcohol
I should note here the chips tend to "sweat" grime at this point and I usually will take a modified soft bristle brush to the chips dipped in 99.9% alcohol to the chips and dab them with disposable rags to soak up the residue.
3) I then bathe the board in distilled water, agitating the water for a few minutes. The bath has a grounding point to earth just in case.
4) I lightly blow air through the board, then remove all the chips into anti static. My compressor has dried air and is grounded to prevent static.
5) Next I repeat the flux remover and alcohol bath followed up by a light brushing with a modified soft bristle tooth brush
6) I bathe the board again in a new batch of distilled water. Agitating over about 30 minutes. and repeat again with another batch of distilled water. 

The problem for me with putting something in the dishwasher besides my wife killing me is that I cannot inspect what is going on and it can "force" water into places that is shouldn't be. You can see the colour of the water or ISP at every step. I do use the dishwasher to clean key caps...

After all that about 40 years of grime is just gone.

Finally I use the compressor to blow air though the board and they tend to look brand new.

Then of course is all the fun of getting them to run, but in the case of the work I'm doing risking the run with layers of caked on dirt or bug bodies isn't an option.

BTW: I also used this same technique on all my other systems that are grimy. I guess it costs me about $30 is supplies, but the results are worth it.

Cheers,
Corey