Mercedes SLK R 170 does not always start

Hello everyone! As described in the title, when the car has stood for a weekend it does not start any more. The following I tried so far: – new batteries in the radio key, has brought something for about 4 weeks – K40 relay card soldered, built in, car starts on – next day but not again – new battery built in, after about 4 weeks again the problem What else could be the error? When soldering the K40 I also noticed the following: One of the Ste If you change the fuse, it looks like it’s right in the holder. But if you take off the panel so that you can see the circuit board directly, you can see very well that the fuse presses the socket into the housing. Only as further information, that the K40 likes to make stupid.