My Revo Premier, probably 4 yrs. old, with little use, screams like a banshee when I cast it. It still cast well, and there is no unusual noise when retreiving.
Any ideas as to what's causing this noise, and/or fix.

Worst case scenario, send it to Abu and they will take care of you. I've sent old reels for customers and I have yet to be charged for a repair.

Either the bearings need to be oiled or replaced

What Tim Said,(Baylor Guy)

Bearings need to be cleaned and proper oil put in them. If you have not oiled your bearings in 4 years then the next thing will be your worm and pawl.

I put a drop of yellow Rocket Fuel on each, and no improvement.

Did you flush them out with lighter fluid before adding oil?

Did you oil the one on the end of the spool itself. YOu would need to remove your spool to get oil to this. The one under the adjustment cap has little to do with this. If push comes to shove make sure you have oil in the cast control cap and in the palm side base under the bearing. If dry or dirty this will allow the spool to scream from the ends of the shafts but not likely.

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