So a few months ago, I had to order an entirely new steam knob and valve shaft for my Isomac Cappuccina, who's rubber seal had degraded from the many tightenings over its years of use. What I noticed after a few months of using the new shaft is that the new seal degraded to an extent as well, making me need to over-tighten it to stop dripping, and starting the vicious replacement cycle all over again.

Without further adieu, the solution:

What you need:

• Plumber's tape (thicker is better, but thinner is fine too)
  Scissors
  Patience

Instructions:

1. Get your steam adjustment valve shaft out.

2. Cut a fair amount of plumbers tape into a long strip the width of the seal.

3. Apply the tape in the opposite direction in which you insert the knob (most likely counter-clockwise), until you notice a protective layer of tape has formed over the seal. Replace the valve shaft back into the machine as usual. It should not only protect the seal, but make it such that you have to tighten it less to stop leakage.

4. Repeat when you notice that the tape starts to wear.