I have reels that need regular maintenance, depending on how much use they get.
My saltwater Medalists get cleaned and lubed after each and every use ( which is a pain you know where).
Most just others get a good cleaning once a year.
Break them down only as far as you feel comfortable with. You need lots of light and a good large work space. There's little pieces to lose and springs and even ball barrings that will go flying if you're not careful. Following schimatics
is best, but you can also take pictures and always pile your parts in the right order. Maybe in something like an egg box
I use a toothbrush and machine (3in1) oil to clean everything but if you really need to clean up an old relic, soak it overnight in a very
mild vinegar solution, then brush it clean
Hopefully you can put it back together the way it came apart.
You'll want to lube the moving parts with a reel lube like Quantum Hot Sauce
. There's other brands too. I think the reel lube that I have came from Penn or Mitchell. I've also used a very light coating of axle grease. You just don't want anything so thick as it attracts dirt and sand.
The best thing to do is a rinsing after each prolonged use.
One of my reels builds up salt behind the drag plate. That's the last and hardest part to remove. It's very difficult to break down that far to give it the cleaning that sometimes needs, especially if things are getting corroded.
It's far easier just to give it a little attention after each use