<VV> no reverse pg

[shortle]

Tech help needed:My 63 Rampside PG has been working beautifully when all of a sudden I have no reverse. Fluid is full and VERY clean (I am religious about clean fluids in all my cars). Any thoughts/suggestions? If it is rebuild time, is Clarks video a good source for info? Any other references out there for tech support? I have all the factory manuals but am hoping for more. Thoughts, please. Thanks, Tim.