Any chance of a picture. From your description (the leaves have rusted a little and stuck together) they fold out from a pivot, something like feeler/thickness gauges.
If that is the case, I'd go with George's suggestion of Diesel but add Kerosine (50/50) to thin it out and help it penetrate.
Something thin like a scalpel to slip between the leaves and separate them (little by little) and re-soaking would help as well.