Cal 1861 erratic Timegrapher reading, what can be the cause? Update

Hi, i got this 1999 Speedmaster 1861 yesterday, gave it a full wind and after wearing it 16 hours + 8 hour dial up rest, it lost just 4 seconds.
But on the Timegrapher dial up 12 sec interval i get this ;

- 39 / - 7 / -27 / + 17 / + 17 / - 41 / - 1 ?? Any idea what is happening ? looks like Shakin' Steven.

My cal 861 Speedy reads fine and has a steady straight line so i think the machine is okay.
Thanks for your thoughts !

The quick answer is that it obviously needs a service.

Thanks all, and yes definitly should be cleaned and serviced.

The main issue seems to have been that the 2 holding screws on the movement / enlarger ring were loose. So there may have been some extra or double vibrations as now that it is thight again the reading is a whole lot better. I got the timing regulated to Around + 5 sec p/d while wearing it, so on the wrist it is fine for me, but the Timegrapher stills shows a fluctuation curve from fast to slower and back again, changing per two 12 sec interval timingperiods. Not like the staircase of the picture above but more fluent.

This is worse with a full wind and almost gone in the 2nd 24 hour of power reserve, but is the torque/pressure on the train (much) weaker in hour 25 trough 40 of the PR ? Beat error remains around 1 ms and amplitude is still good 240 - 260.
Can the crown be the problem and somehow not transfer the ticking correctly ?

Thanks for your thoughts !