Back off your drag when not in use. Keeping your drag locked down can flatten out the washers. I don't think that's happened already, but it's good advice for the future.
The non-carbon fiber drag washer in Shimano low-profile reels is pretty lousy but again, I doubt anything has happened to it already.
Did you just spool up straight braid? Braid can slip on the spool, giving the illusion of a weak drag.