Always check the toe board clearance first. If the pedal is too far away from the firewall, the cylinder can't refill completely from the reservoir.
Get a recently manufactured master cylinder repair kit, if you haven't already. Not NOS or something that sat on a shelf for years.
If the pedal is still soft and there are absolutely no leaks, including wheel cylinders, you need a new master cylinder or re-sleeve and hone the old one.
Also, Speed bleeders are cheap, safe and super easy to use.
A good brake system is and stays firm 100% all the time.
No need to pump to build pressure, at all.
Bleed the brake lines annually, if you drive much or little, to get the moisture out of it.
