Most of my equipment is used off my boat but surprisingly, they get doused quite a bit. I find that regular hose downs after each trip with a gentle spray from the garden hose is most important. Then a couple of times a season on the ones that see the most use, I open up and clean with either Salt X or Boeshield T9 corrosion inhibitor then re-oil and light grease. At line changes and at the end of the season, I strip all the line off, clean the reel extensively and coat with a film of the Boeshield T9. This stuff can be left on or wiped off after application. In the off season, I leave it on. It creates a waxy film and will prevent any corrosion. I know, I know,I'm anal. But, I don't want to replace everything every couple years. I just like adding new stuff.
I know some people spray everything down with WD-40 and some say it can be used as a fish attractant. I'm not convinced of that. I've always been told not to get gas or certain oil on your hands then handle your bait because it'll drive the fish away. Don't know if it's true or not.
But, WD-40 is made from petrolium distillates. Again, I don't know. Maybe the stuff I recommended is too, but they work for me. I've got a Pen 650SS that's getting a little long in the tooth and it still looks and performs great.