Case 580 Super K stuck in forward position

I have a case 580 SK that is stuck in the forward position. This is the second time this has happened, the first time it was stuck in the reverse position. I removed the floor plate to gain access to the forward/reverse valve on top of the transaxle. I disconnected the shift linkage and removed the detent so the spool could move freely but that didn't change anything. The spool feels like it is hitting something metal, it is a hard stop. After turning the spool and pushing and pulling, it suddenly freed up. I reassembled everything and started the machine. As soon as I put it in the forward position, it got stuck again. The machine runs fine and I can shift it through all 4 gears in both forward and reverse position. I just pulled the valve body off the transaxle hoping to find a problem. Even after removing it from the transaxle, the valve was still stuck in forward. As soon as I turned in over and laid it on my work bench it freed up and would move through all 3 positions (forward, neutral, reverse) again. I removed the spool and cant seem to find anything that would cause the problem. I am wondering if the spool is worn allowing side movement inside the valve body which is causing the spool to get stuck. Can anyone offer any suggestions? I am at a loss... I have researched this issue and cant find anyone talking about it on the web. I believe that the valve is a Berg Warner but cant find any information on their site either. I originally posted this in the Case & David Brown section but realized that wasn't the best location (this is my first time posting).

A 580SK should have Carraro transaxle,first thing I would check is the neutral start switch it may be jamming up stopping the spool from moving,if that checks ok dismantle the valve to see that there is no foreign material or something come adrift in the valve,you can look up the online parts catalog for the 580 at the link below.
AJ
http://partstore.casece.com/us/

Thanks AJ for your advise! I did check the neutral start switch hoping that was the problem but even with it and the detent removed, the spool wouldn't move. I have the valve off and apart looking for debris but couldn't find anything obvious. I didn't realize that it was a Carraro valve. I will track that down to see if I can get some more information on specifications. I am worried that either the spool or the valve body is worn allowing the spool to hit inside. Have you ever seen or heard of this issue before?

I've had trouble with the control rod but not the valve itself,I doubt if the valve been worn is the cause but, take it apart and see what you find,shake it about to see if anything loose inside.
AJ