There is an oring and a seal on the cylinder levers. The only way to fix them is to pull the top cover off the hydraulic unit. You then need to remove the bolt and washer that holds the cast iron arm on each lever on to its shaft. Then remove the turnbuckle link that connects to the 3 point lever, and the 2 bolts that go into the side of the hydraulic unit where the hydraulic levers meet it. They should now slide out and apart from each other. You should find a lip type seal on the outside end of the inner lever, and an oring on the inside of that same tube. Those will be the culprits, but you'll also need a new gasket for the hydraulic cover, and 12 new orings for the oil passages that go from the main housing to the cover.

I have the cover off my 1655 right now, I'll try to remember to take a picture of it. I just replaced the same seals on it.