Yea, I believe there should only be one swivel, above the sheave for the jib halyard. I could see how that might cause some problems. First thing I would do would be to try without the bottom swivel. Also, furling the jib is much easier when the mainsheet tension is released, it will definitely bind if the main is tight. Also, turning downwind (particularly in high wind) allows the main to blanket the jib making furling easier.

Regarding the forestay, it was probably not shortened. The adjuster plate on the 18 allows for a lot of adjustment. It may be a good idea to replace all shrouds & forestay if they are old (best to replace all at the same time).

sm