Intake Valve Leak? Options

[Qoognish]

'74 1.8 in fair, but driveable condition. I bought the car recently as a project to learn from. I'm no slouch for mechanical things, but still very green when it comes to cars.

After a valve adjustment and oil change, and before I replaced the plugs, I figured I should do a compression test for good measure. 1, 2 and 4 were all good at around 115-125 psi, but #3 tested out at 90psi. During my first shake out drive, I was able to get the car up to ~75mph, but that's about it. Acceleration seemed sluggish, which I assume has something to do with the 'bad' cylinder.

I performed a leak down test on a cold engine after double checking the valve adjustments when finding TDC on #3. Leak down showed ~45% leakage.

While under pressure, I laid a tissue over the oil filler port and no movement, and no sound of air. I couldn't hear anything through the tailpipes either. Under the car, I could hear the air flowing on both sides of the engine, but couldn't pinpoint anything. I removed the air cleaner boot and when I opened the throttle, the sound of airflow changed drastically.

My best guess is a leaky intake valve.

My questions are: 1) am I right? What else could it be? 2) What's the easiest, band-aid fix and what is the proper fix? 3) Is it okay to drive as is until I have time and money for the iminent rebuild of the engine?