My Fisher 400 has a very smooth fluid feel when the FM tuning knob is turned. In contrast, my 800B's separate AM and FM tuning sections feel a little gummy when turned. The FM on the 800B has a little more resistance than the AM when turned. I'm guessing this is a lubrication or dried grease issue with the separate tuning mechanisms. There are a series of pulleys as well as the turning capacitors. Is this a common issue and what is the best approach return the tuning mechanisms to the original smooth and fluid feel? Where is the most likely location of the resistance?