This am SWMBO and I stood in the garden and pulled the tags on our old Crewsaver manual jackets. The cylinders are at least seven years old and quite corroded, although we manually inflated the jackets two years ago.
Anyway, both went satisfyingly pop and inflated perfectly. Left them for eight hours or so to make sure they weren't leaking then fitted new cylinders. Dead easy to repack them as well, and we tested the whistles for good measure.
An easy job for peace of mind, total cost £20 including free delivery for the two cylinders. (From AQUATOGS)
Why am I posting this? Because it was easy, cheap and had a relatively high feelgood factor. Not so often these three come together in the yacht maintenance universe, so if your old jackets haven't been serviced for a while why not give it a go?