What Lube do you put in your Columbia S/W Speedo Changer?

[Boryca]

Here's my problem: I've got a few of these Stewart Warner speedometer changers - rectifiers as I like to call them, because it seems that's what they do - and I can't figure out what type of grease should really be used in them. They chatter at high speeds, almost exclusively in OD, and do it more when cold. I'm assuming the multipurpose grease I'm using is too viscous, but it works better than some of the thinner things I've tried.

So, what do you use in your speedometer changer that keeps it quiet and healthy?

Mike