Firstly don't touch it yourself. It sounds as if what lubricant there was has dried out leaving a sticky residue behind. You won't have the equipment and tools to dismantle the shutter and ensure the speeds are accurate afterwards. Take it to a reputable repair engineer and get them to service the lens and the camera body as well.

Being of mechanical construction they will have the skill and know-how to take it all to pieces, clean it, lubricate the shutter and set the speeds afterwards. It will be money very well spent.