NOT having to readjust your toplink is one of the subtle, but greatly rewarding and satisfying feelings. It is just one of those things. I can tell you from experience now.
As Kenny mentioned, it's usually the valve and not the cylinder that causes what we see as "leak down". When I got my first hydraulic toplink from CCM, It was rock solid for all the road maintenance and building I've done. Well, somehow I managed to knock the DPOCV off.

So I re plumbed it direct, without the DPOCV. The cylinder still works fine, but I've noticed that the angle I set my boxblade at does change slightly over the the time it takes to make one pass over my 1/2 mile long dirt road. This may not seem like a big deal, but I'll tell you it makes a difference. Before, I could set the boxblade perfectly and drag it to smooth the road ... enjoy the forest and animals, have a sip of coffee and smoke a cigarette. By the the time I reached the end, I turn around and do the other side back up the hill.
Now, if I don't keep an eye on it, I find it starting to cut and build up dirt in the box. I can accidentally re-shape the driveway when I don't want to. So I have to look back and constantly (strain my neck) check and re-adjust the boxblade to have it smooth like I want. I'm putting the DPOCV back on! I know my valves aren't as good as yours, but it's a poor man's fix for that problem. And it's not only my rear remote valves either. My backhoe stabilizer legs were constantly leaking down after I parked and removed it from the tractor. This was a real problem since it was very hard to put back on if everything did not line up just right with the subframe and all. So I added DPOCV to them and man, that hoe stays in the same position now. I've left it for over 4 months and it didn't move at all.
After I got the CCM toplink, I added my own hydraulic sidelinks and another valve for additional rear remotes. I put DPOCV's on them too. And also on my QA hydraulic gauge wheels, which are really the rear wheels for my rotary cutter. They don't change position unless I move them. There are several places to get DPOCV's and if Mark at CCM has extra ones, I buy them from him and use them. But they are Metric so be prepared to deal with adapter fittings to mount them. They are much smaller and work great. The
Surplus Center ones work great too, but they are about 3 times bigger than CCM's.
Hope you don't mind me sharing some photos of my DPOCV's on different cylinders.
These are on my backhoe stabilizer legs.
They are CCM's and are very small and compact. They fit nicely in tight places.
These are from
Surplus center. They are what I used for the hydraulic side links and are quite a bit larger than CCM's but don't look that big on these cylinders, since the cylinders are big 3-1/2" ones with 1-1/2" rods. Their cracking pressure (or pop off) is rated about the same as CCM's.
This is another CCM CPOCV used on the hydraulic gauge wheels.
They keep the level of my rotary cutter or boxblade or rake right where I set it.
Notice also that the DPOCV's are all hard mounted to the cylinder itself.
