Hello,
I also ride a used Racer-X. Definitely get yourself the rear shock pump, and also download the manual for the rear shock. It's a very useful manual (assuming you have a Fox rear shock, that is).

My rear shock does leak slowly - not enough to bother me on a single ride, but I do have to pump it rather frequently. (I'm not yet willing to find out how much it would cost to resolve this problem...)

So, I have to check my rear sag frequently - how far that rubber ring moves when you compress the shock by sitting on the bike. The manual recommends that when you sit on the bike, the sag should be 25% of the maximum travel. I also do a more aggressive pushing of my body weight down on the bike (for "maximum sag"), and I prefer to have the ring go no lower than 2/3 of the way down.