Hi Steve
Clean the inside of the cylinder with brake cleaner type stuff. Check it for any pitting at all. Brake fluid can attract water given the right circumstances and any sitting water, even a miniscule amount can cause pitting (rust).
The rubber parts are hard to assess the condition. I'd put a kit in just in case. A kit is a lot cheaper and less painful than a brake failure and crash!
This is one area of motorcycle maintenance where it pays to be picky in my humble opinion. Others may say to clean and reassemble and if it doesn't leak, it's good.
Hope this helps,
Richard.
