Do I need to worry?

[95 Smoke Pole]

Maybe I'm just an worried new owner of a 95 psd but....well here's the story...I pulled a friends fifth wheel about 200 miles back to his home yesterday (I bought his truck a month ago and agreed to use it to bring his fifth wheel back to his place) anyway after we backed it into his driveway
I noticed some fluid on the road, it looked like it had just started leaking when we started backing up. It looked like tranny fluid (i'm a total novice at mechanics). When we looked under the psd we noticed a small amount of fluid leaking from what appeared to be a "by design" hole in the bottom of a housing...see attachments...the leak stopped and I started the truck this morning and no leak, the tranny fluid level is fine.. is this a "normal" thing to happen after hauling a trailer?