K-50 problem

My k 50 with 10k on the shutter gives me a dark shot for the 1st exposure but then is fine for subsequent shots.

Is this the beginning of aperture block failure?

Yes

That’s the symptom of the aperture failure.

"Only" about 10k (or fewer) actuations over a "few" years seems to be a consistent factor in K-30/K-50 Aperture Block failures = not enough regular and frequent use.

Mine (currently for sale) is just over a year old and I use AA batteries all the time. As it has 3500 shutters on the clock I think it has a few more years in it yet.

Unfortunately, if the truth be told, there is a lot of "evidence" on the US forum to say that very low use may actually be a cause of the problem because the solenoids in the Aperture Block assemblies then just don't get "exercised" enough and both the magnetic and mechanical "stiction" build up.

The fixes are now well-known, and that's why my K-30 already has had a "new but old" White solenoid fitted - I don't think I actually ever saw any positive proof of the issue but there were several instances when, on reflection, the initial first shot symptoms may have occurred (and that was at rather less than 10k actuations).

I am pleased to advise that my K 50 has now been fixed ,free of charge, by CR Kennedy.