This may be old news, if so sorry. Until last week I had only one fluid leak on the 40 and that was the GM power steering pump (my T-case started puking a few days ago ). I decided that since I was working on steering stuff anyway I'd try to fix this too. A trip to my local Ace Hardware found me in the plumbing isle, where I ran across a 1.5" Slip Joint Washer. I already knew the diameter of the reservoir filler neck 1.5" so I decided to give it a shot. The washer is very pliable and fit perfectly inside the cap. The cap fit on very snug, so I pressed down on it and turned (much like a medicine bottle) and when the tabs on the cap seated it fit very well. Later in the day I had to pull the pump off the rig so I decided to "test" my fix. Prior to draining the pump I loosened the upper mounts and rotated the pump 90 degrees........no fluid leaking from the cap. a $.59 fix for a very annoying problem.