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No those old pumps are not air tight. Nothing on an N is air tight! Unless you include the tires. You should have determined what was wrong with the lift before you took it apart. Here is a file I have about trouble shooting the lift. BEFORE DOING ANYTHING TO THE LIFT IT SHOULD FIRST BE INSPECTED FOR ANY INTERNAL LEAKAGE. GOOD ADJUSTMENT CAN BE DONE WITH A LEAK IN THE SYSTEM BUT FOR GOOD OPERATION AND IN ORDER TO TAKE FULL ADVANTAGE OF GOING INTO THE LIFT IT SHOULD BE DONE FIRST BEFORE ANYTHING ELSE IS DONE. I will send you some of my previous post files about the lift. I think that you are probably having a combination of problems which is common to the 8N lift. One of the worst offenders is the cam follower pin which is what the position control receives it's input from. The other thing is to look for a leak in the sysyem @ the ram cylinder rings etc and the pressure relief valve. Also there could be a gasket leaking somewhere such as under the ram cylinder where it mates to the lift cover housing.
If you dicide to take the lift off to work on it be sure not to remove any bolt except for the ones around the outsides of the cover. If you should remove a bolt that has fine threads it will be from the inside pattern and you should put it back in the same hole it came from. You can remove them after the cover is on the work bench if it becomes necessary. You should first take off the right hand inspection plate under the seat on the side of the lift housing.With an implement on the lift start the engine and with the lift in the up position look inside and see if their is oil leaking from the end of the lift ram cylinder.If their is only a slight drip this is normal.If their is a fairly steady stream this may be the trouble.If the oil is coming from somewhere else try to pin point its orign. If you find no appreciable leaks on top in your view then you may have a pressure relief valve leaking. It is located just under the pto shaft on the vertical back of the pump.Sorta shaped like a spark plug and an 11/16" box end wrench fits it. You can check it for leakage by first finding it with the engine off and then with the pump running and with a load and hot put your finger over the end of the relief valve and if it is leaking enough to be a problem you will be able to feel the oil push your finger off the end of the valve slightly.You can check it by washing it up and then soaping it real good with some dishwashing detergent and water and apply air to the end that goes into the pump. If it is leaking you should replace it with a new one. The part # used to be 8N638. Hope this will give you some starting places. Zane in Al.
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