Hey,
Unfortunately, sounds like you've chipped your tip. The spiralling and rough finish, also possibly a wierd sound are tell tale signs your tip is toast.

There arent too many places that can re-do your tip. Unlike Carbide tips, the diamonds cant be easily re-ground. In reality the only thing that will cut the diamond is a bigger diamond!

You can look up a few engineering places that do diamond bits for heavy machinery, maybe they can help, but in my past experience, I haven had much luck with them. Get a strong magnifying glass and have a look at how its damaged, sometimes a litlle creative shimming of angles will give you a new edge to work with.

I've gone thru 3 diamond tips in my racing lifetime, and Ive probly been around for long enuf. I had a mate who chipped his Hudy tip pretty badly on his lefthand lathe, then we shimmed it up on my right hand lathe and it was perfect. A year or so later I chipped it, then made do with another tip. Till I got a new lefthand lathe, so i tried it again on my lefty and its perfect again! Hows that for luck!

So. do what I said, inspec the tip, you might be able to adjust the tip angle and height to make it work again. Strips of aluminium can work good!