I would tear it apart and give it a good cleaning to start. Lay the parts out in order as you take them out. Put them back in the same manner. Key things to check are the spool bearings, wear and tear on the internal nylon parts, and the brass raceway in the side cover. All the parts you need can be ordered directly from Shimano in Irvin, CA. I use silicone lubricant to degrease and clean the internal parts, dry off and reapply the appropriate lube to the parts. For the raceway use Brasso to remove any oxidation/discoloration. I use 2 types of lube, one is the light oil that comes with the reel for use on the bearings, raceway, level wind, etc. The other is a heavier grease used on the gears and the drag system. If you don't have them you can get them from Shimano. Also, schematics are available for use on the Shimano website if you have trouble getting it back together. Hope this helps.