The three capacitors (on each motor) are there for noise suppression. These were beneficial when running with 40 MHz radios/receivers (75 MHz, here across the pond).
If you are still using the old radio equipment (i.e. 40 MHz), then you should keep them.
If you are running newer 2.4 GHz radio/receiver equipment, the noise suppression won't matter (to the best of my knowledge). It isn't going to harm things to leave them in place. If you replace the motors, you won't need to add them (as long as using 2.4 GHz equipment).
In short, it depends on the radio equipment being used today.
As for inhibiting the motor function, these capacitors should not affect the motor function. If the motor is working intermittently, the motor brushes/contacts or core/windings may be bad.
Sounds like an old motor that has deteriorated with time. May need to replace.