AL 390 Tired

Well after 12 seasons of duck and goose hunting I took apart the spring tube assembly in the stock of my AL 390.It was a messy sight with the spring,the spring rod and parts of the tube in various stages of rust.After scrubbing, cleaning,lubing and putting the gun back together, I now have a single shot rather then an auto.I can feel that the spring is not working too well.I can't believe the gun worked so well for so long, rust and crud must be a good lube! My question is: Should I replace the whole tube assembly or just the spring? The spring is very rough but the little metal rod it attaches to (on the receiver end) felt corroded also. May be too much friction in the tube???Thanks.