Magnum 425 won’t go into reverse

I had a guy message me about a garden tractor I’m selling & offered to trade a 1996 magnum 425 that looks to be in really nice shape, is suppose to run and drive really well, goes into high & low just fine, but will not go into reverse.
I’ve never wrenched on a Polaris that old & am looking for some insight on what the problem may be before I get back to him.