Thank you Teo.
This is an excellent topic and wonderful advice.
I love this part of your post
If you know every small screw, every little pin of your machine, only then can you know what you must do. But if you just know a little and experiment, you risk a great deal, because the machine is very complicated. There are many tiny screws which might easily be broken by a strong shock and which cannot afterwards be brought in any shop.
...And I know that my hardware-store does not sell any of the replacement parts.
Thank you yogionefromobie for your reply. It is very informative and useful.