Bronica S2A shutter problem

I got my Bronica s2a out of storage after 20+ years of retirement (the camera, not me), and it seemed to work fine for a while. After some 6 or 8 rolls of film it started to develop a problem, it appears to fire allright, but when I forward the film the two parts of the shutter curtain separate a little and by the time the shutter is fully cocked there is a gap wide enough to let light through to the film just above the mirror.
Does anybody have experience with this problem? could some informed DIY effort cure it? The camera is otherwise in a very good condition and it would be a shame to discard it.

It just needs to be cleaned and lubricated, and I'd leave that to a professional. Bronica shutters are particularly complicated. I've sold mine, but I usually sent them to Frank Marshman (camerawiz). Koh's Camera also specializes in Bronicas.

Thank you for the advice, I'll try and find a repair shop here in the UK and I'll report the result if there is going to be one.

I had my S2A shutter repaired by Don Clark Camera Repairs, Wotton-Under-Edge, Gloucestershire (01453 842102). They are very good and not too expensive.