How to remove metal filler

[john]

I’d like to get rid of the black stuff here - liquid metal, I think. What tool or fitting will let me get in the mast track gate and remove it efficiently? mast is still up.

 

[Malish]

A Dremel and time

 

[waynes world]

Yep Dremmel or Die grinder

 

[Yngmar]

Router with appropriate bit.

Why is it there in the first place?

 

[Poignard]

I would use a keyway chisel and a hammer