Hi everybody, I followed wlachan's and violini's instructions for reaching the (potentially) problematic parts. Last night I needed nearly two hours, because I was trying to be careful and don't brake something as it's only plastic, plastic and plastic inside. (I didn't broke anything, but nearly lost some pieces). Sorry for the poor picture quality. My P.S. camera is weak at high ISO and forgot to turn it off
So, I removed the front plates and the bottom metal cover. And I got to this:
(click for bigger)
The gears from the film advance motor. Everything seemed OK. I continued the disassembling.
I removed 4 separate gears and the odd one (it can swing a little bit left and right) with its parts (the plastic screwed part and the little gear beside). That "odd" gear can swing a little bit left and right (it's between the black one in the middle and the white one on the right and I didn't took a photo of it disassembled).
The most tricky part was to reach the part that wlachan marked on the photo. there's a tiny little screw on this part (see photo below) and I was afraid not to brake the bigger plastic part.
I almost lost the small parts when they fell on the floor. They slipped when I managed to safely unscrew the screw.
After that, I cleaned the sensor and I cleaned the gear with the metal parts on it (they touch the sensor). I used common alcohol. All the gears, so far, seemed without a damage.
I put back those parts back.
And I started to put back all the other gears. I used a blower (for camera) to blow any dust and checked if there was any damage on them. Every one of them looked OK.
And the photo with everything put back.
I have yet to put an empty film and to test it. I put in it an old test film to see if the camera works again. Everything seemed OK. I shot it through the end of the film, it re-winded it nicely. Every function on the camera apparently worked etc.
If the problem is not solved, I guess that the only other possibility would be the advance motor itself. I guess it could be also changed. I'm not sure how I could be certain if the advance motor is the problem (of course if this doesn't solve the problem).
I would be glad if wlachan and violini (or anybody that is interested in this) gives an input/opinion/comment on this reply.
cheers