My tire recently went flat on my Wizard Hydrastatic lawn mower and had to take the tire off to get it aired up. When got the tire off, the axil came with it. With that, oil (I'm assuming gear oil or hydrastatic fluid) came out, I got the tire aired up but now the tire will not lock in and comes out easily also the gears will not engage?

There is a clip inside that holds the axle inside the transaxle.
Remove the transaxle, clean thouroughy, and open the transaxle housing up, then replace the damaged clip, reinstall the transaxle and go back to mowing.