A little dab of waterproof marine wheel bearing grease on the plungers will make them last nearly forever. In a pinch I have used waterproof sunscreen. I think Vasilene works too. The grease lasts the best though.
I became a believer when I replaced one of my 17 cams and the very first time I popped the rudder it stuck down. I studied the situation for a while and found that the plunger was bone dry and it just didn't work like that. I put some grease on it and it has worked perfectly ever since. The cams don't work dry. When you get a new boat there is a little dab of blue waterproof grease on the plungers.
If you grease them and they still don't work. Check the plunger hole in the casting. If there is too much slop in the hole the plunger will move forward instead sliding up and down the way it should. I haven't had to do it myself but I would fill the hole with marinetex epoxy and drill the correct size for the plunger.
cheers
Bill
