I have a through the roof attic fan that may have seen its last days but I wanted to check. Very very slow to start up and when it gets going, it squeals like crazy. I'm guessing something with the bearings/motor. Sprayed with WD-40, no real improvement. Thoughts? Does it need to be replaced from on the roof?

Depending on the fan size and the WD40 used it could be a fire hazzard at this point. WD40 can be flammable. Another thing is it may be cheaper to rebuild the untit then direct replacement. Id this a belted unit? If so you will want a new belt to go with it also.

Fan blade diameter is about 12 inches. Item is not belted. I believe unit is about 15 years old.

If everything else looks good then Im sure its time for brushes and bearings if it has them. Bearings for sure. Check pricing in your area. Rebuilding should be much cheaper route to go.