What is there to check on the ariel ? Have frequently checked the SMA connection into the box itself which seems fine and the ariel stays where it always is.
Cheers
If you have a second aerial it would eliminate an aerial fault, maybe in the lead or sma connection. From what you say though, it sounds as if your problem lies elsewhere.
I agree with you that after a period you know your own box and it's little idiosyncracies and you can spot a change in performance a mile off.
Grasp the nettle Wayne - get it off to the menders.