I love Dairy Queen and make a point of grabbing some whenever I'm in town but there's still a lot of locations and I'd suggest you check out a different one.
The staff was very nice and open to giving extra hot fudge for my Oreo Brownie Sundae but it didn't seem just a "little dirty looking." Maybe a lot can happen in a year. I actually wondered if one can get sick from unsanitary conditions at an ice cream place.
Don't give up DQ but maybe try one somewhere else.