Re:
Old hoods contain silicone oil which eventually comes out of them as you wash them and grab them also
they start to dry up and there's not much you can do about it other than find replacement hoods.
But I've tried a few creams to soften them back up and the best I've found is E45 cream.
One other major factor is direct sunlight and heat also ruin hoods, keep the hoods out of direct sunlight
and keeping a bike in the shed is a bad idea due to the heat which can build up during the summertime.
Just out of interest, what type of hoods are yours ?