Dear Knockolgy community,
Here I am, once again asking for some help to identify a specimen I own, but was bought when I was too young to understand properly the world of writing instruments — and when the internet was way less effective and useful than it is today. 
Long story short: it was probably around 1995 when I was introduced to the magically fine tips of Pilot G-Tec C4 pens, and fell in love with their amazing writing experience; since then, I never changed my mind, and I still write almost exclusively with G-Tec C4’s.
A couple of years later, I think it was around 1996-98, the owner of my local stationery shop suggested me to trade the plasticky, expendable bodies of the G-Tec C4’s for a more sturdy and stylish all-metal barrel, one “made to last forever”, with replaceable tips & cartridges which could be bought in stock and swapped once the ink had run dry, or used up. This is the pen I bought, and it came with cartridges slightly different than the ones in the regular G-Tec C4’s (they had a “lid” in the back of the ink reservoir, and a different structure of the tip section — yet the very writing end was the same):
If I examine the pictures, and some other detail shots I put below, I find a lot of similarities with the later Pilot Cavalier Gel-Tec Pen, but I’m quite sure it was not a Cavalier; I think I remember vaguely something like a “DX” on the cartridge wrap, but might be wrong. So, what is this mysterious pen? Any chance you might know the product name and code?
I’ve used and loved this pen for ages: it was with me during all my years at university, and I tried to care for it as much as I could, even though it was an EDC item, and as such it was exposed to any sort of challenges, from falling to the ground to being scratched by other things I kept in my pockets (see the dents and scars in the pictures).
After serving me as the best of the soldiers for much longer than both the stationery shop owner and I thought possible, almost suddenly around 2010-2013 the pen started to show alarming signs of failure: the thread connecting the grip part and the rear barrel part eventually became loose, and I could not tighten it anymore, so I decided to retire this pen and leave it as a museum piece.
I still have some leftover cartridges for a Pilot Cavalier Gel-Tec Pen which should work fine with this pen, see picture below: I’m almost sure these were not the original cartridges for this pen, but they fit the tolerances and should provide the same delightful writing experience.
So, my final point is: does any of you happen to know more about this pen, and maybe have a piece of advice as to where I can find a replacement? Even a Cavalier Gel-Tec Pen might be fine, but I’d really like to find an exact copy of my beloved gel pen barrel (same anonymous grey-ish colour, same unimpressive round accents, same sanded grip section, same perfection embodied into a pen).
I plan to open a dedicated thread in the Market section with details concerning a possible purchase or trade, so please let us keep this conversation just to fill in the gaps regarding the identity of this item.
Regards!