Just reviewed the posts on this topic. I have lots of the TWSBI 530 and 580 demonstrators and one Mini. No problems yet, but they're lightly used over the years. Several years ago, I purchased a smoke-colored 700. From the start, the piston moved back and forth fine, but no vacuum was created, so no ink went inside the pen. I followed instructions with the pen, disassembled the relevant vac parts, put in some fresh silicone in the appropriate place, reassembled, and still no vacuum. Rather than hassle with customer service and delays, I used a ready solution: I have lots of hypodermic needles left over from 1994-98, when my son (now 40) was 14-18 and took growth hormone shots. I remove the nib-and-feed, inject ink into the vac reservoir (holding the pen upright), then reinsert the nib-and-feed. That works perfectly. As the pen holds lots of ink in its reservoir, this is a practical solution. Of course, had I had the patience, the best long-term solution would have been to get the pen fixed.
I had the same problem with a Turquoise-Blue Visconti Wall Street FP with the vacuum-filler that I purchased from a pen store in Honolulu (owner had passed away and his family was selling off inventory). I did not test the pen before the purchase (my bad). But, again, I used the same procedure as described above, and it worked with the Visconti, which also has enormous ink capacity.
So, in essence, I treated this pens with defective vacuum fillers as eyedropper fillers with great results. I would add that if you can get a hypodermic needle shot, it is much easier and more precise to use than an actual eyedropper. You just clean out the hypodermic with water for reuse later. Emptying and cleaning is no problem, interestingly enough.