'72 1.7
The Turtle is my daily beast. She gets driven to work at least twice a week, 75 miles round trip.
Driving to work yesterday and she just ran like crap.
Got home, ate dinner, then went out to see if I could find anything.
Started pulling the plug wires off to pull the plugs so I could do a leakdown, and #3 wire was off!
Awesome! There is my problem!
I do a leakdown once a year or so just because that is the way I am, so I decided to still do the leakdown and see how the engine wore this past year.
4% last year, and this year was 6, 4, 20, 4. Holy !#@$!!
A little air was coming from the exhaust, but most sounded like it was coming from the leakdown fitting.
Reconnected several times with the same result.

So after my long winded intro...

Could a dead hole prematurely wear like that?
What kind of damage do you think was done driving ~75 miles on 3 cylinders?
If not leaking from the leakdown hose connection, where could the air be coming from and sound like it was coming from there?

I will put back together tonight and test drive, but would love to have a plan of attack just in case.

75 miles is a long way on 3 cylinders.. More than likely unburned fuel washed the cylinder down and has created some of this.

I'd do a valve adjustment, since you heard some air escaping the exhaust valve. That may indicated a tight valve on that cylinder and that can easily lead to the leak down.