Speedometer cable to 904 automatic transmission

Their are two "0 Rings" on Speedo attach point, on the 904. One of them is leaking. remove the whole assy, find something to plug the tranny case, cause fluid will leek out fast.
get new "O" Rings, and install on speedo assy. Very easy job, except for the leakage.
Hope this helps. Do you have a fac service manual,????. They come in real handy.
Dave