I would still suspect the capacitors still. The older logic ICs in these are super-sensitive to spikes on the rails. If you have some suitable lying around you can tack them across the existing capacitors and see if it makes a difference.
I had a counter of similar construction by Heathkit (who are related to Schlumberger) and the thing had an internal oscillator that was broken resulting in a new one being built. Worth seeing if the internal oscillator and integrator/comparator are doing what they are supposed to as well.
See thread here:
https://www.vintage-radio.net/forum/...d.php?t=136242