I don't know whether this will work because I haven't tried it, but if the "POS clicker assembly" is indeed, a POS clicker assembly, then risking wreckage of the plastic parts of the POS clicker assembly shouldn't be a concern.
If I was to disassemble a Slimline Pro with a goal of avoiding damage to the barrels and as much of the hardware as possible, this is how I'd approach it:
No prying with a screwdriver or anything. Prying will wreck it.
I'm assuming you have a transfer punch set, too.
1. Have a component set in front of you for reference
2. Unscrew the clicker button/finial from the plastic clicker
3. Unscrew the nib and remove the inkfill.
4. Stuff pea-sized pieces of wadded paper towel to fill up the inside of the outside plastic piece of the clicker assembly. You'll know how big the pieces need to be by referencing the component set in front of you.
5. Stuff and pack a few more pieces into the upper barrel. Use the largest sized transfer punch that will pass through the nib coupler and attempt to tap out the clip assembly. Steady firm taps are better than angry hard taps. Think "Woody Woodpecker", not Paul Bunyan.
6. Keep tapping.
7. Seriously. . . keep tapping.
8. Maybe the inner plastic pieces and the spring in the click mechanism will pop out, leaving the outer plastic piece inside. Maybe that's not a bad thing, yet.
9. If the clip assembly shows signs that it's coming apart from the barrel, keep tapping. If the inner part of the click mechanism and spring pops out, fine. . . let it and the paper towel pieces come out.
10. Whatever the case in #9 (hopefully, the clip assembly came out), screw the nib back onto the nib coupler.
11. Insert the largest sized transfer punch that will pass through the upper barrel but not through the hole in the nib.
12. Hold onto the upper barrel and begin tapping the transfer punch. I don't know which parts will separate first. It might be the upper barrel from the center band (ideal!), it might be the lower barrel from the center band, or it might be the nib and nib coupler from the lower barrel. I sure hope it's the center band from the upper barrel, and not the center band from the lower barrel.
13. If the upper barrel separates first, then grip the lower barrel and tap out the nib and coupler.
14. After tapping out the nib and coupler, insert the largest transfer punch that will fit in the nib end of the lower barrel and tap out the center band.
15. If the upper barrel didn't separate from the center band in #12, then you might be able to use something like a dental pick or fashion a small hook to pull the outer piece of the plastic mechanism from the upper barrel through the finial end.
16. If you get the remaining piece of plastic out, then you should be able to tap out the center band from the upper barrel as in #14.
It's possible that you might be able to push out the two inner pieces of the click mechanism all the way down to the nib end, and push it out through the nib coupler. If that is successful, then skip the wadded paper towel and start at #10. If the upper barrel separates from the center band, then you should be able to extract the outer plastic piece of the click assembly and tap out the click mechanism .
Again, I haven't tried this. I'm going by what I'd try if I had to disassemble a Slimline Pro. The wadded paper towel technique might end up destroying the plastic. That's a risk you'll have to take.
Pffft. . . now I want to rummage through my completed Slimline Pros, find the ugliest or most dissatisfying one, and give this a try.
