Do you have any rubber on your filter?
I have a Fluval 205 and swear the "rubber" parts are silicone. I use vaseline on the "O" rings and since starting using it in October last year have not seen or felt any of the clasic signs of degrading (perishing) rubber....
Rubber is generally not used as it hardens with age and so becomes inflexible and cannot create working seals. It is sometimes used on the pipeing inlets/outlets.. but these are only designed to be fixed into place once in their lifetimes - so any hardening simply fixes them better into place.
You shouldnt need to lubricate moving parts of the filter - and if you do as a matter of maintainance then the lubrication should be no more than literally a smear.. not even enough to wipe back off. They are designed to lubricate themselves with the water flowing through them. As long as you keep the parts free of dirt and any deposits then they should be good for the life of the motor.
Are you having a particular issue?
