Kind of depends on the condition of the leather. If it's crumbling, probably not much you can do. I'd try a damp cloth to remove the mold. I get the feeling that much of it may not be meant to be flexed. If parts of it like straps, etc., are still pliable and not dried too much, a good quality leather conditioner might help it (I use Leatherique on my vintage car leather seats).

I have a few old steamer trunks that crossed the Atlantic before WWI,and the leather trim and straps on them are too far gone to restore.

Hope this helps a little,

vince