All of them will hold air over night but they do not shoot the same. Some would have a louder pop, while others do not. Even though new seals & a new pump rod seal was installed. I would adjust pump rod for minimum head space. You can't over do it though, because of the air bleed hole. If you cover the hole, not as much air would be allowed in on the pump stroke. The pump cup/rod on these pistols was not a good design. O-ring pump heads I think would work better.
Also sometimes they would leak between the rod tube & air chamber tube. That is when I have to resolder them.
Your stock should not be made of only walnut.