How to tell when a vibe pump is on it's way out?

[Steem21]

Dear all,

Since I have the recent pleasure of owning a well cared for Silvia, I have read that vibe pumps have a life span of about 4-5 years. This one is about 3 years old and going strong. I was curious as to what the signs and symptoms of a vibe pump going downhill would be? Oh, the previous owner had the OPV adjusted to 9bar - will this prolong the life of the pump too? Also, is the only way to check whether the pump is putting out the right pressure by using the pressure sensing PF's?

Thanks

Steve