That is really bad news Len. I have checked my pistol, which has the standard issue black grip, and while there is no sign of cracking (yet) the grips do seem to have pulled back somewhat from the grip frame edges.
I also notice that my grip plates no longer lie flat against the frame and are bowed out slightly. Luckiy l had left the grip screws quite slack when I last took it apart, otherwise there could well have been some cracks developed.
I suspect (but can't be categoric) that the grips were hot pressed from a thermoplastic polymer which contained too much plasticiser (usually butyl phthalate). Over many years this evaporates and the plastic shrinks. The plasticiser loss is accelerated by contact with absorbent materials, so was the particularly bad side the one stored face down, perhaps on cloth?
I have encountered another problem with the MAS 50 - the black finish on the frame fades slowly when exposed to light. The frame is aluminium or aluminium alloy, so it was probably blacked by anodising and dyeing with an organic dye. Such dyes will fade in light, whereas traditional black on steel last forever. Some time ago I decided to display my pistol in a wall cabinet. After about three years later, I found that the exposed side was a significantly lighter black, almost grey, compared to the underside. So, it came off the wall and is now always kept in a drawer.
The MAS is a nice pistol with some interesting features, but was evidently not made with longevity in mind!