Been looking over the Sealed Unit Assembly. Especially the check valve. I can understand wanting to use a ball bearing for the exhaust valve but going to the trouble of using a ball bearing on the check valve is just beyond any comprehension. There is not possible way that this expensive ball bearing check valve will in any way improve performance. Plus, there are some basic problems associated with servicing this valve. As is, as part of the removable Sealed Unit Assembly, it's still a chore to get out the valve seat AB-504. Procedure is to insert a special screw into the valve seat and then punch out the seal by tapping on the screw from the other side. Not a lot of fun, but, imagine if it wasn't in a removable unit. Pulling the valve seat while buried inside the gun would be a feat of magic. I think it's possible that the idea of a Sealed Unit Assembly may have come about for concerns of getting at the check valve for servicing.