Booleans causes holes

 From:  Swegmang (ACMS)
8382.1 
Hi, I am still learning moi. I am getting holes after I do Boolean operations at a certain point. I've heard that you cannot fix this which seems to me like a big deal if thats the case.

Any advice on how to deal with this? I uploaded the 3dm file. Try booleaning the main shapes.





I appreciate any help and advice.