Rear End Leak - Sunstar

I picked up a Simplicity Sunstar a few weeks ago. Mows like a beast! I keep it up at my farm about an hour from our house. When we got there today I noticed a wet spot under the back of it. Looks like fluid is leaking where a hose fitting goes into the rear-end or transmission housing. My question is should I try to tighten the fitting or is there likely an O ring or something that needs replaced?

Also, where & how do I check the fluid level to ensure I haven't lost too much?