Just got my Sheaffer Triumph 1250 vac-filler back from Francis Goosens ("fountainbel" is his nickname on FPN) in Belgium. If you search on FPN, you'll find threads discussing a piston unit Francis has invented that replaces the worn-out system in old pens of this type. The advantage of his approach is that the unit inserts from the back end (whatever it's called) of the barrel, so one doesn't need to remove the nib and section. That's important because, as I understand it, removing the nib and section can be a very delicate and tricky operation with the triumph nibs, and sometimes the section and/or barrel can break.

Francis says that another advantage of this unit is that it actually works better than the original mechanism. With the old system, Sheaffer recommended not using more than a single downstroke. As Francis writes, "Using the original sealing set-up it was recommended by Sheaffer to push the plunger only one time quickly down & NOT to apply repetitive filling strokes.
This recommendation aimed avoiding leakage on the plunger rod seal by excessive back-up pressures. This risk is fully eliminated using the “fountainbel” cartridge.
I obtained filling volumes up to 90% by pushing the plunger once quickly fully down & then pulling.& pushing it quickly up & down 5 times over a reduced up & down stroke of 12 mm ( half inch)"

In my experience, just two strokes were enough to fill the pen (at least as far as I can tell: after two strokes, there was no light coming through the translucent stripes in the barrel.) There's a very satisfying puff of air on the downstroke, more pronounced than on another vac-filler I have.

The whole process was pretty quick except for the shipping from the U.S. to Europe and back.

So I highly recommend Francis' service. If you prefer to do the repair yourself, he also sells his cartridges, as well as a tool that helps extract the old plunger mechanism (he says it works well for 50% of these pens; for the others a little more effort is required.)

I love this little pen! The nib is buttery smooth. As soon as I can borrow a camera, I'll post a pic.

Don