Case 580CK Boom slowly dropping

I have a 1967 Case 580CK. The boom on the backhoe does not stay up (running or not-running). Even driving it around I have to reach behind and pull up the boom every minute or so or it will drag on the ground. I don't see any obvious leakage from the boom cylinder (though could be internal). There is leakage around the control valve (well there is leakage in the area, it is hard to tell if it is the boom sector specifically in the valve cluster).

My question is this. Is the most likely...

Case 580CK Boom slowly dropping

Case 580CK Boom slowly dropping