I too have changed out the JD to the ISO setup many years ago on my 4840. Changed out the IH tractors from their OEM setup to ISO as well and have to say, those were some of the best dollars ever spent.

 The leaking lever o-rings is a common thing and is a pita to fix, but not so much as to make it neccissary to delay the repair. Just get a second set of o-rings when you buy the parts so you have an extra one when you screw up the first ones. It takes patience to get the lever back in place without chunking the o-rings.

 I do wish extreme pain and harm to the idiot(engineer) that thought up(engineered) the expanding soft plug idea to cap the top.