many other answers over here as well
You dropped it and from the look of that pole you definitely don't take care of your equipment
Hi Dave I agree with you, the seal is broken or somewhere it is cracked or broken it may later form one large bubble or not but it is unusable at this point. Most rods this can be replaced.
If not you can use a hand held bubble. It's always a good practice to have a hand held bubble with you it can serve as a good check on any other built in rod bubbles. Most surveyor use one on their level rods that are not made with one. Now checking if a rod bubble is plumb, that's another story but a very important one.
You need to replace the bubble unit. It would cost you around 5$ for it. I have plenty in stock if you need them. My mail id is [email protected]