This oil fired hot water baseboard furnace was installed in 1963.
Most of the time the problem occurs after the thermostat is satisfied. The furnace turns off for 15-30 seconds than turns back on for 15-30 seconds and may do this up to 6 times.

The repairman does not find the problem since it does not do it when he is here.

Could be a thermostat heat anticipator problem or one with the aquastat. If the thermostat is one with a mercury bulb, I'd replace with a digital. Cheap, easy, & might work. At least you'd have a new & probably more accurate stat.