Hi Larry I've seen this happen lots of times on these trucks and its normally an easy fix. 2 things to check.
First make sure you check the oil level with the transmission at operating temp and the engine running

1 look for a small breather pipe from the top of the transmission that goes to the transmission filler about 2 inches below the dipstick these are prone to blocking and if it blocks oil will push up out of the filler tube.
2. If the breather pipe isn't there change the oil and filter I've seen blocked filters cause this problem as well fairly regularly

Finaly make sure you useJD40 (tractran 9) and not regular ATF (Dexron 2) the recommend change for the oil and filter by Hyster is 2000hrs or every 12 months I worked on them for 19 yrs and would stick to this