[Richard and Rhonda]

How do you know they need replacing. You named one obvious sign, leaking oil.

The other way is dirty but effective. Do the usual safety things when jacking up the bus. Disconnect the bottom shock attachment points. Move them up and down by hand. They should move slowly and take a good bit of force to actuate. If you feel any slop in the up and down movement the shock needs to be replaced. If you feel one of them that doesn't require as much force to move, then replace it.

It's hard to tell just from driving one that the shocks are the culprit.