Not strictly computer I know but I'm sure someone on here can help.
Basically do LNB's "wear out"? Mine is a Sky one that has been up from before the youngsters left home about 15 years ago and I cancelled Sky. I was getting pixelation before this bad weather and have checked the dish orientation. Nothing has moved (marks on the mast etc).
Unfortunately looking at it it is a one off shape ie the mount is rectangular not round so it looks like a new dish and everything if I do change it!!
LNB's can fail at any time and come in various types. The mount that attaches the LNB to the arm is usually rectangular. LNB's and mounts are usually supplied separately. If you look at the Maplins site it will give you an idea of the prices click here but you may be able to get them cheeper via the web.
Note: check the cable for any faults. Cracked/split cable will let water in causing problems. The F connector at the box or dish can become loose also causing this problem and last the box can also fail.
A very small movement can make a big difference.There will be a built in signal strength with which you can check/adjust the dish if it is accessable .Sometimes a tree can grow into the line of sight reducing the signal strength.