A good sewing machine grade oil is fine for all these tasks. Should your reel have a disk drag with a cork surface, place a couple of drops of Neet's Foot oil on the cork and let it soak in. This will keep the cork from drying out and chipping away. It also helps keep the drag working smoothly. Lastly, if your reel was assembled with machined screws rather than rivets make sure they are tight.
Few things are worse than having the reel body drop away from the reel foot while fighting a fish.
Leaders Monofilament leaders do deteriorate over time, even if not exposed to UV light. Replace them with the onset of the new season. You should only have to do this once if you use tippet material on your leaders. You can save yourself quite a bit of money if you simply add tippet material to your leader as the original tippet becomes too short. Use a double surgeon's knot to attach the tippet.