Does anyone know or have drilled the rotor cup?
If so what size drill bit and how many holes?

1/4" hole in every slot

Remember that even though you drill holes in it so it will drain ,it is not sealed , so water will still get in through the shaft and the side plate.You will need to take it apart and clean/grease it if it goes into the water enough that you need to drain the rotor cup. Also since this is the time for big fish , a friendly reminder to take apart your drags -keeping careful track of the order of the washers , clean them good and get all that evil salt outta there! It builds up pretty fast even if you take good care of your reels.

1/4" hole in every slot

And, don't try to drill thru the lead :humpty:

I went with 3/16 holes.Why?Don't really know,just did it that way.I also drilled a hole(1/32?) in each slot on either side of the lead counterweight.

And what Joe said.I had a ton of build up especially after fishing last week.