Ive been using one for the last couple of seasons and always wondered if the line roller has a groove in it by design of it i grooved it with my line.

You grooved it... Dried Salt residue in the braid.
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Ok... now my turn... When does the roller need replacing?

when you want it to. If it starts to fray the braid bad its time. I had the deepest line groove in my roller but it didn't really cause any problems due to break-offs.

I kinda like it actually.

Ok... now my turn... When does the roller need replacing?

when its grooved...mann....or making wierd noises...

I would replace it. Don't want to take any chances. Im on my third roller now...

There should be a slight depression, or groove as some call it, in the roller if I am not mistaken. Mine have always had one even on brand new rollers.