Cellullar antenna connector comes off instantly

I recently "repaired" my wifes iPhone 4 since it wouldn't pick up any WiFi or Bluetooth signals. That worked perfectly alright.

Unfortunately, since then she has bad or no cellular signal. I checked the antenna connector and it seems the uFL connector does not stay on its socket any longer, if I put it on again, the phone will have excellent signal until moved and loose signal then.

I tried to reattach it several times, but it never stayed. Do I need to replace the whole antenna or is there some kind of trick to fix the connector?

Thanks a lot!