Class rollant 66 losing pressure

I have a class rollant 66 round baler. I pull it with an IH 1486. The problem I am having is keeping the down pressure up. If I am not constantly pushing the hydraulic controls down the baler will not keep pressure. It's not a major problem except when the bale is almost full it wants to keep making a bale and won't signal the bale full indicator and it's a pain to constantly have to pushing down the hydraulic controls. It still makes a great bale. I was just wondering if it might be a tractor problem or a baler problem. We used to run it with a new case 95 and had the same issue it just didn't lose pressure as quick. Thanks for all feedback

Class rollant 66 losing pressure