How good are you at reading schematics?
You just may have to find the cap/resistor - or part - that is in the TX chain causing the low wattage.
So, inspections are in order - any noticeable fresh work on the foil side of the board? Wires that don't seem right - most Cobras have a wiring harness "Loom" where all the wires are tied together and placed to one side of the frame or chassis the board rests in- look for wires soldered with heat shrink or electrical taped in the harness itself - that means repair of a mod done then retied off. These can be places or areas where problems like yours can occur.
Was a modification done to the "Spike" diode - the big one by the Audio Modulator (Transformer) - so that it seems to have some kind of adjustable carrier to make wattage adjustable up or down (like RF gain or Dynamike - does this wattage or carrier adjust instead of what it is supposed to do?)