The gearbox most likely has a check plug on the side, just stick a screw driver in there and look at the fluid. If it's clear, not milky or dark and dirty, you're good to go.
My first tiller was used, well used. It was a front tine and they beat the crap out of you. Those things can rip your shoulder out of the sockets on hard ground. I got a few years out of it, then it threw a rod. The next was a Troybilt Pony, a 5hp rear tine unit. I used it for 20 years and gave it to my son. The engine (Briggs) was shot and he put a $99.00 Honda knock off on it. The last one I bought is a Troybilt 6hp with a Honda engine. It should outlast me
When you break new ground set the depth to 2"s and once that's done go deeper. It will be easier on you and the machine. I also let the machine cool down some when doing a large area. The gearbox is what gets hot as all the power is going through it.
Edit: As cold as it gets there, now would be the time for next years garden prep.