Airguide Troubleshooting

My port speedo was DOA when I bought the boat this spring. I have been fooling around with it all summer - first discovered that the original airguide pitot was missing the brass insert in the end. I filled the hole where the brass plug was with silicone and the speedo came to life for a day, but was reading low. Next time out, it was dead again. Replaced the pitot with a new venturi-type unit from Skidim, and the speedo came back to life, but was reading low still. It died halfway through the day.

When I removed the tubing to connect the new pitot, quite a bit of water came out. I'm guessing that's not normal...Should I suspect bad pitot tubing, or a leaky connection somewhere in between the speedo and pitot? Any suggested steps to continue troubleshooting? I was thinking of disconnecting at the speedo and blowing compressed air back through the line in case it is partially clogged somewhere. Could this harm the balance tube in the stern? Advice much appreciated, thanks guys!

Thanks Pete, so if I understand it correctly, a leak in between the pitot and the speedo allows water to fill the line, instead of air pressure building to operate the speedo? By "balance tube", I actually meant pulsation dampner. Wasn't sure what it was called, thanks for setting me straight. Thanks for the heads up on the freeze damage! I do have a cup or so of water in the bilge after a day on the water...i'm guessing if the dampner is cracked, I can probably solder it to repair?
Time to take a peek and see if I can find the issue without pulling the fuel tank...