It certainly sounds as though that is the problem.
You can remove the sear very easily without a full strip of the pistol and examine it. The sear slides vertically in a machined slot against the action of a spring. It is probable that the end of your sear that engages with the piston is worn and rounded or possibly a bit has broken off. It is usual for such items to be case hardened and so restoring its profile would not be recommended
Best to buy a new one
J Knibbs or Chambers should have new ones in stock
ATB
John