Dubravko,
I have restored many old receivers and most components tolerate water fairly well. You do not need to use distilled water until the very last rinse of the chassis.
I would suggest removing the panel meters, bezels, paper labels and transformers that may become saturated and can be cleaned by hand. You can use a stiff bristle brush with hot water and a mild cleaning solution similar to a product sold in the US called "Simple Green". Do not immerse; get the chassis wet with water and use a brush dipped in hot water and simple green to scrub the exposed areas that are dirty. It should take you no more than a minute or two to scrub it down.
Immediately rinse with several liters of very hot water by splashing it with some force over the chassis to carry away the dirt and cleaner. The last rinse is with boiling hot distilled water as it does not leave behind a residue. Use compressed air to blow the water out and off of the chassis.
If you have an oven, pre-heat it to around 80C and turn it off with the door closed. As soon as you finish blowing out the chassis with compressed air it should go in to the oven for approximately two hours. After two hours, take it out of the oven and again use compressed air to dry/cool the chassis down to room temperature. Then put the radio chassis in a dry, well ventilated spot in your home or workshop and leave for two days.
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Looking at photographs of that particular radio I would try to keep the water away from the audio transformer and you may want to loosen up the side plates covering certain circuits so they dry out completely. The magnified viewing bezel might need some special protection as well.
When done, try to blow air in to the IF cans and the trimmer capacitors so there aren't any shorts.
http://www.la6nca.net/tysk/e10k/index.htm---------------------
I always wanted a Telefunken Köln E52a-1
http://goto.glocalnet.net/bosradio/telefunkenE52eng/E52photogallery.htm