Remedies for Stiff Action
Silicone Spray
One of the most common complaints from people who have bought used Rhodes pianos is that the action of the keyboard is stiff or sluggish, even when the piano looks like it's in mint condition. One way to smooth out the action is to apply a fresh coat of silicone spray on the key pedestal felts, which are glued to either the underside of the hammers or the top of the key itself (see Figure 2-1, 27 or Chapter 8 in the Service Manual). The factory originally used Krylon 1325, which is no longer available. Krylon recommends using Sprayon S01324 as an alternative from their current product line.
Note that other sprays may contain solvents that can melt the plastic hammers. Steve Woodyard recommends that if you're going to use a different brand, test it by spraying the side of one of the hammers to see if there is a reaction. (And if there is one, don't use that spray!) This treatment will make the action much lighter. Afterward, you may need to change your playing style slightly, in order to avoid overstriking the tines.
Teflon
Tim Nelson offers an alternative solution: Teflon powder!
I'd like to put in a plug (again) for the suggestion made by my piano tech for restoring/improving the action for my Rhodes Mark I: dust Teflon powder onto felt bearings of the action (instead of using the Krylon silicone spray), using a small brush. This is the treatment used on acoustic pianos by many techs. Teflon powder is available for this purpose from piano supply sources, but probably not at the local hardware store. The powder becomes embedded in the felts, making them silky smooth. It is more time-consuming and more expensive than using the silicone spray, but if you're crazy about your Rhodes like me....
And for those who can't deal with the powder version, Peter Hayes recommends TEFLON SPRAY!!!
Another vote for Teflon. I've been using Elmer's Slide-All spray lubricant for about a year or so on my Rhodes restorations. It's a spray-on Teflon lubricant. I will also use Hoppe's Powdered Teflon (Schaff Piano Supply has this) when I can't find the Slide-All. I lightly coat key peds & cams (butts) and a little in each key bushing. I dig the feel and my clients dig the action.