QL17 GIII shutter problems

[Daan]

I bought a QL17 GIII a couple days ago, but there seems to be a problem with the shutter. Whenever I try to use a shutter speed under 30 the shutter sticks. It opens but doesn't close. With higher speeds the shutter works normally. There's no problem with the apertures settings.

Does anyone know how I could fix this?
Do I have to open up the camera and how would I do this?

Thanks!