Compressed air (use a compressor) without a water trap, causes some condensation to form. It is not much and it requires a closed room and some time to form. That is all the "water" needed to clean up really dirty units.
First step can be an outdoor cleaning with compressed air and a tight nozzle. All dust, fibres, whatever, is better blown outside rather than your workshop. A paintbrush (or an assortment of 2-3 brushes) to focus on specific hard points helps a lot.
Second step, focus on the bench and blow piece by piece. Care should be exercised not to blow things into tuning capacitors (wide blade clearance allows debris to get trapped inside). Condensation helps to "wet" really dirty spots and clean them up with the air. A thin paintbrush can be useful here as well.
Step three, optional and on occasion, depending on equipment configuration: Add on boards can be removed to be cleaned individually for best effect.
Last resort: washing: Years ago I received a Revox PR99 unit. It operated more or less but had issues with the brakes and noise in pots and switches sometimes didn't engage. It was stripped down to pieces (the build of the unit allows for that) and the main PCB (a passive PCB with traces but no components) was brushed with dishwasher detergent in the sink repeatedly so that tar and nicotine would be removed. I also washed the individual pcbs that included even relays. Under the sink, using a paintprush and a toothbrush.
After washing and rinsing with tap water, I rinsed the pcbs with isopropyl alcohol to help remove water and salts. Following that, they were air dried in the oven at 40C/100F for an hour or so. Checked on them from time to time with the compressed air. If any liquid was blown out, they needed more baking.
I would, however, never attempt to put an entire unit in the sink and wash it. Too many things uncontrolled and too many possible locations water should not go without control.
Contact cleaner should only be sprayed under control to the correct points only. Revox switches can be disassembled and cleaned individually. Fixed switches, if on a switch block, could be cleaned in an ultrasonic bath or you can spray contact cleaner through any holes on them but it's hit and miss no matter how much cleaner you waste. And these cleaners are not good to inhale so pay attention.