Fluid in bottom of speedometer?
 

What would cause fluid to accumulate at the bottom of the speedometer? It looks like it was slightly greasy and has been gone for a while, but you can still see slight discoloration on the white parts at the bottom of the gauge. Any ideas? I figured it must be the sender leaking.

gear oil coming up the cable.

Thanks John. I guess the cable must need to be changed.

Cable has a seal that can fail. It keeps the oil from being wicked up from the trans to the gauge.

You'll need to clean out the crud in the gauge.