I have a Pila that showed similar symptoms - here's what the problem was in my case...
Each spacer has a small diameter threaded stud, which screws into a thin (couple of threads worth) metal plate. The stud is not threaded for its entire length, and the unthreaded portion is of lesser diameter and is located next to the body of the spacer.
If you have a spacer where the unthreaded portion of the stud is far enough forward of the body of the spacer, and you tighten the spacer too much (intending to get solid electrical contact) the threaded portion of the stud will go right through the plate.
Then you're faced with the interesting challenge of applying enough force to get the thread to engage from the wrong side while backing the spacer out. Of course, this is compounded by the limited access to the body of the spacer when installed, and the grip-unfriendly plastic of the spacer's body.
It took a good deal of moaning and fussing, but I was eventually able to get the threads to engage and get the spacer out. I considered disassembling the charger to make it easier, but that wasn't possible without removing the spacer. The approach I used was similar to what you tried with a penknife, but it had to go beyond the gentle stage.
I haven't seen any other report of this problem, so maybe it's relatively rare, nevertheless I think this is the biggest weakness of the Pila design. The spacers' ability to thread into place is a good idea, but it's not really well implemented. Even if you don't have this problem, the spacers are still too fussy to install and remove.
I ended up making my own spacers from machine nuts & bolts - there are more elegant ways to do it, or you can buy ready-made spacers for this purpose, but what I've done is solid, it works, and I was able to do it the same evening.
- Syncytial.
P.S. - This thread may get moved to the Flashlight Electronics forum, as that's where discussion of chargers normally takes place.
