Pen running dry

Here's an annoying problem. I hope someone has an easy fix for me.
BTW I'm kicking myself for not finding this group years ago.

My daily workhorse is a perfectly adjusted (luck, not adjusting)
Sheaffer Prelude. Writes like a dream with a nice wet medium line -
for about three pages. Then, the flows starts to dry up, the colour
turns lighter, the nib scratches until about a page later when it
becomes a nail with no ink. At that point I have two choices. Either
let it rest for a day or so, which will bring it back to normal, or
twist the converter FORCING ink to the nib.

What's up with that? Is this normal, is there a fix? None of my
other Sheaffer's do that.

Thanks.

BTW - who's a reputable person to do tine adjustment on an older
Imperial that's become mis-aligned? How much will that cost?