The Parker Duofold has been around, in one form or another, for about a hundred years. It started with the 'Flat top', the most famous of which was the 'Big Red', this was followed by the 'Streamline' version, the button filler, the AF, the Aerometric, and now modern cartridge/converter versions. The so called 'Aerometric', this pen, was introduced in 1953.
It is not a difficult pen to disassemble, as with most pens the difficulty arises when bits that should come apart easily don't, due to them being clogged with the residue of dried ink or the overenthusiastc application of glue by a previous 'restorer'.
Removing the filler sleeve involves some gentle wiggling and pulling, preferably after gentle heating, I use s hairdryer for this.
The old ink sac can then be removed and the nipple to which it was attached cleaned. Be careful not to break the breather tube as the old sac is removed and retain the thin piece of plastic rod, this is a simple 'agitator' for the sac contents.
The nib and section can usually be pulled out using a suitable piece of gripping material. If it won't move then try a little more heat, perhaps a turn in an ultrasonic cleane or a soak in water may help. If it still won't move then use a knock out block, with great care.
To dismantle the cap press the cap stud firmly against a rubber block, or some other high friction material ad turn the cap to unscrew the stud, it is a right hand thread. A suitable flat bladed screwdriver can be used to remove the brass bush to release the clip and complete the disassembly.
After a thorough clean and check the ink sac can be trimmed and the pen reassembled and tested.