The screw-in base is slightly misaligned with the stem. See photos. Perhaps a washer would help.

It looks like the previous owner also tried to unscrew the top tulip portion, so it too is misaligned from the stem. Please see photos.

I tested to see if it holds water, and it does, but I don’t know for how long, or how quickly before it will rust. Long term, it might be better to insert a glass or plastic test tube instead of pouring water directly into the vessel.