The mechanical clocks require regular maintenance and service. The hardened steel pivots pass through brass plates, and this metal-on-metal contact can and will wear over time, ovalling the holes in the plates, and eventually causing the gears to jam and stop the clock from striking, chiming, or timekeeping.
Oils dry out over time, and attract dust. This, in conjunction with particles from metal wear, make for an abrasive paste which wears both the brass and the steel.
Just like with mechanical watches, you cannot oil a dirty clock, and the clock must be fully disassembled to be properly overhauled and cleaned.
Most clocks, whether in Flea Markets, or Antique shops, will require service, unless they have been overhauled and have a guarantee. 99% of old clocks are neglected, and the maintenance period of 8-12 years has been forgone, resulting in sometimes extreme wear and tear.
So definitely do get your clock serviced, and it will last many hundreds of years. Definitely do not spray the works with oil or WD-40, this will cause damage. Also do not place Kersosene in a cup inside the clock case, or apply to any part of the metal works. Oil must not be applied to any gear teeth, it only attracts dust and dirt, and the gears grind themselves up.