1946 to 1969
The peak of the fountain pen before the ballpoint won. Parker's 51 went to the Aerometric filler in 1948, Sheaffer launched the Touchdown in 1949 and the Snorkel in 1952, and Montblanc's Meisterstück 146 and 149 piston fillers set the shape of the luxury pen. Cartridge pens caught on in the 1950s and 1960s. Fillers from these years are easier to live with, and many pens survive in good working order, but a sac or seal that's never been replaced will still need attention.
15 pens we cover.

Parker · 1948–1969
AerometricAero-metric filler, 1948 to 1969
Post-war golden age
$130–$270 typical ask
31 on eBay

Parker · 1964–1994
Cartridge and converterSterling silver crosshatch, 1964 to 1994
Post-war golden age
$140–$210 typical ask
37 on eBay

Parker · 1964–2007
Cartridge and converterBrushed stainless steel, from 1964
Post-war golden age
$55–$90 typical ask
30 on eBay

Parker · 1948–1965
AerometricMark I, 1948 to 1951
Post-war golden age
$25–$40 typical ask
34 on eBay

Parker · 1948–1960
AerometricShorter 51, 1948 to 1960
Post-war golden age
$100–$190 typical ask
10 on eBay

Montblanc · c. 1950–early 1960s
PistonCelluloid, 1950s
Post-war golden age
$1,275–$1,625 typical ask
5 on eBay

Montblanc · 1950s
PistonCelluloid, 1950s
Post-war golden age
$725–$1,050 typical ask
11 on eBay

Montblanc · 1950s–1960s
PistonGold-nib student pen, 1950s
Post-war golden age
$190–$290 typical ask
24 on eBay

Sheaffer · 1952–1959
Snorkel and TouchdownPalladium silver Triumph point, plastic cap
Post-war golden age
$75–$170 typical ask
10 on eBay

Sheaffer · 1952–1959
Snorkel and TouchdownGold-filled cap, 14K two-tone Triumph point
Post-war golden age
$180–$250 typical ask
4 on eBay

Sheaffer · 1959–1968
Snorkel and TouchdownPlastic cap, gold-filled band, 14K inlaid nib
Post-war golden age
$260–$320 typical ask
6 on eBay

Sheaffer · 1949
Snorkel and Touchdown1949 only, Touchdown filler
Post-war golden age
$85–$210 typical ask
15 on eBay

Pilot · 1963–present
Cartridge and converterClick-action Capless, from 1964
Post-war golden age
$150–$230 typical ask
35 on eBay

Pilot · 1964–1973
Cartridge and converterFirst-generation pocket pen, 14K nib
Post-war golden age
$110–$180 typical ask
28 on eBay

Pelikan · 1956–1965
PistonThird version of the 400, 1956 to 1965
Post-war golden age
$260–$340 typical ask
24 on eBay