I just got a Parker 75 with a Medium nib, possibly 1970's, as the nib's marked with a letter and the tassies are dished, but it's incredibly dry (see sample).
I already left the nib and the section soaking all night (not much came out), and then a few hours this morning, in warm water with a drop of dishwashing soap. There was some serious muck under the nib (at the tip of the feed), which I used an exacto knife to remove - you can see some of it in the photos, and there's also some in the slots where the nib slides into the feed. After the two soaks, it's somewhat better, but writing with this pen is still anything but pleasant. I suspect there's more dried ink between the nib and the feed, but I can't get to it unless I take the assembly apart.
I've disassembled this kind of nib before. It took a bit of coaxing, but it was doable. This one, however, isn't budging one bit and, of course, I don't want to break anything, so I'm curbing my super-powers for now.
I still have to try 10% ammonia, but that'll have to wait until I'm back home tonight, as I don't want to do that for more than an hour at a time (unless some learned expert considers that it's OK to leave it for longer periods - and how long, btw).
Does anyone have any ideas or suggestions on how to remove the nib from the feed?