Replacing Santana Air Knobs

If you can find these things... they're like gold! If not, then here's a really workable and easy solution for anyone that has one or both missing.
Many years ago, a lot of spas were manufactured with these air control knobs, and they're not produced any more...

First, get a replacement air knob Assembly that will fit "Inside" the existing socket.

Now, remove the securing nut from the assembly, and push it down into the existing socket. Make a measurement as to how much of the new assembly sticks out..

Using a hack saw, saw off the bottom of the cylinder by that amount.. Ensure that you have a good fit...

Now, using silicone sealant, put a bead around the inside of the existing fitting just above where the new cylinder will bottom out.

Using sealant again, put a thick bead of silicone around the bottom of the cylinder.

Carefully insert the assembly into the fitting, ensuring that it stays centered.

Rotate it so that it faces the way that you want it to. Do the same thing for the other air valve, and let the silicone cure for at least 24 hours before moving or attempting to adjust them