Help! Visconti D'essay Disassembly And Piston Repair

[geistag]

Hello! I've been recently given a Visconti D'essai by a friend and although it was solt to him as a NOS, the piston seems to be jammed (or perhaps the rod is broken?).

 

Turning he piston knob seems to do something inside because it can only turn so far on one dirrection or another,but the piston stays put at the middle of the barrel. Now,the problem is that I have no ideea how to disassemble the pen and I was hoping that someone around here knows. I've tried soaking the whole pen (with the nib and feed pulled out) in water with dish washing detergent, but to no effect. I also tried to push on the piston from the section side but I didn't dare push it to strongly and it didn't budge.

As far as the disassembly goes, the piston knob has no retaining pin (as in an Aurora 88k or a Luxor Grand Visible) or any sort of grooves or flat sides for a sort of key to be fitted and then pulled apart (as with the 149 or m1000...) also I tried heating the section to try and pull it out as in the old fountin pens and still nothing.

So as you can see I'm struggling with this mint beautiful example that simply doesn t work.

Please leave any suggestions especially if you have disassembled simmilar piston fillers. Thank you!