Benjamin / Crosman H9A, HB17 air problem

Hello and thanks for reading. I am new here and am hoping some folks here may be able to help me out.

I have a Benjamin Crosman H9A .177cal (HB17 I think) series pistol that won't hold air more than a few seconds. I pump it six times and it'll fire a pellet out of the barrel if the trigger is pulled immediately after pumping, but if I wait to get on target it won't move the pellet out. It just makes a weak spring type noise. I am assuming that it has an air leak. I have read around online that it needs oil (which I have ordered) but im not sure where to put the oil to fix the problem...if in fact this is the problem. Any help would be greatly appreciated, thank you!