Sealing the collets to fix a stem seal problem works to a degree but is not good enough if the engine is run at idle for a long period from a cold start. But good for normal use.
Have used an oscilloscope to monitor the oxy sensor and the sensor seems to work OK but not according to the information on the net. It switches between about .3 to .7 at about 3 cycles per second some of the time, as it should, but then goes through many variations. May need to be under load.
Then tried the test using a portable gas stove to heat the sensor and got an output of up to .7 Volt which varied depending on how much of the sensor was in the flame. It works but not sure how well.
There is a small free computer program which turns a computer into a simple oscilloscope. The sound card is used for the input and the lowest frequency is 20. A simple chopper circuit with high input impedance could be used to record a signal onto tape along with a calibration signal and the recording played back on the computer. That would also record DC signals.