Do not worry this is a simple fix. I had to add liquad to my Gaffrig on a 29 Fountain I once owned.
Go to the local drug store like a CVS, Walgreens ect and get a bottle of glycerin. Take the speedo out of the dash and on the back there is a fill plug. Pour the glycerin in it and reinstall the plug and speedo. Should take all of 15min.
see ya, Mike