I have a larger MF 2660 bought brand new in April 2011. The Nimco loader valve delivered with my DL250 loader would not let you force the tip of the bucket downward. The poor unsuspecting dealer tried several times to "adjust away" the problem, then replaced that $1100 valve. No change whatsoever. Same thing. Agco depot maintenance people totally failed both the dealers and the customers. Eventually (I'm talking a year) I got fed up and went directly to Nimco. They were quite aware of the problem, explained it, sent me the replacement parts (which were very simple to install) and I fixed it myself. So there were bad control valves BOTH on new tractors AND in the supply system. If I were in your shoes I would do the following: 1) Insist that your dealer contact Nimco directly and bypass the brain-dead AGCO system. 2) If they won't , then do it yourself. I'm not saying your problem is the same as mine. I am saying the communication path between customers to dealers to AGCO parts and notifications systems to suppliers like NIMCO are totally broken. Almost useless. Also saying that NIMCO will very likely help you solve the problem.
I can go into explanation of the 4th hose, etc. but let's get your problem fixed first. NIMCO is easy to find on the web. If you have trouble locating NIMCO send me a private msg and I will give you name and phone number.