I agree, and have repaired a few grundig boxes with duff caps,. howver those tended to b around 1999-2004 ish.
i would check the cabling, the F-connector should have the central pin of the cable straight with no strands of screening touching it at all. the screning shoud be in contact with the plug body. see
https://www.youtube.com/watch?v=LzoGX6ef4y8
if there is a badly fitted plug then you will get the problem you have. also check it is connected well at the the LNB, and properly insulated from the weather.