Getting warmer over time is usually a sign of a refrigerant leak. There are other causes , but that would be first on the list.
R12 or 134 don't lose there cooling properties over time ..they leak out of the system.
If the fittings have outside threads with a flare connection , they are R12 . Usually when a unit has been converted , they replace the fittings with the 134 adapters , being an indicator of 134 swap.. Evidently these were not changed , but that does not mean someone did not recharge w/134 without changing the fittings..but on the other hand , if the fittings were changed, it has been changed to 134a..