I would suggest you pull the spark plug on the low compression cylinder and look at the valves to see if they are closing. You can see them with a pin-point light through the spark plug hole, or at least the exhaust. A stuck exhaust valve is the most common cause for a low pressure condition on one cylinder that I have found. It produces all the symptoms you state.
You may be able to solve a valve problem by having the head pulled and valves reworked. A lot cheaper than a new or rebuild.