Thanks for continuing to follow. This time around I restored two Parker 51's. I hope it wasn't too much to do two at once. I'll probably come back around to other examples. Come to think of it, this particular video will have a follow up to demonstrate the quick start up of these pens after days/weeks of non-use. The parker 51 was a really well engineered pen.
The disassembly was overall pretty easy. There were just a couple issues that had to be dealt with - including a big lapse on my part during my initial explanation. However, you'll see the light bulb come one and hopefully this will help you remember this particular detail in the future. There are a couple of decision points in the video as well where a couple things just don't want to come apart, so you'll see a judgement call about whether or not things actually need to be taken apart. It's good to be flexible and use some judgment with these old pens, rather than pushing forward and maybe causing damage to a pen. Overall, these are great pens and it's always fun to work on a Parker 51. Please let me know what you think about this particular video as I did a little more long form take apart so you can see the struggle and minute process.

Things you'll need:
Heat source (I use my trusty hair dryer)
Grippers
Vacumatic tool to remove diaphragm unit
Method of removing diaphragm (dremel with bit vs needle method vs luck that the diaphragm comes out hole)
Soaking solution (water/soap and possibly small amount of ammonia if desired)
Dowel to help push out diaphragm unit - careful here. Soak and take your time.

Polishing materials - micromesh/polishing pad, liquid/cream polish, towels, q-tip, elbow grease, desired was

Replacement diaphragm and dowel - I learned that new materials don't always match the old. Had difficulty putting in a new diaphragm and found that the inner pellet and pellet cup were differently sized than what I've typically seen. Found a work around, but if the pellet comes out intact, it would be smart to swap the older pellet for the newer.
Replacement silicone sac (obtainable at most pen repair sites). You could also consider reusing an old silicone sac - as I had to do. These do last a very long time.
I used a replacement breather tube for the Aerometric - this may not be necessary. These can be found at various pen repair sites as needed.
Silicone grease/vacumatic sealant grease for the replacement diaphragm.
Chalk for diaphragm and sac replacement. Helps the diaphragm slide over itself and it also helps the silicone sac not be caught on the aerometric cover as you screw it back on.

Some links for your consideration:
   • Parker 51  
https://parkerpens.net/parker51.html
https://www.vintagepens.com/Parker_51...
http://www.richardspens.com/ref/profi...