Hi Dennis, I have a mate who fixes my speedo's and tacko's for me, the cause of the needle bouncing around is because there is no silcon damping fluid left in the little dash pot inside your instrument, this is a very small cylinder which is fitted around the shaft coming through to the face of the instrument.
We are able to purchase it from the USA , and the only way to get it into the instrument is to pull it apart and inject a small amount of the silicon damping fluid into the little pot.
He has fixed all my speedo's and tacko's , they now run very steady, the reason the fluid leaks out is because when you place the instrument upside down it slowly leaks out and you'll notice a damp patch around the shaft on the face of the instrument.
Hope this helps you.