[crackle]

I have repaired cracks like this before.
First I used a pressure washer to blast the dirt out of the crack, that should help to mask it, leave for a few days to dry out. Be careful with the speaker grill bars they can be delicate. If all the dirt does not come out you could try bleach as suggested but that may change the colour of the catalin as well.
Then I use very thin runny super glue to try to get it to seep into the crack.
Lightly rub down with 1000 grit to remove excess glue and polish with Bakelite polish.
Then if you wish roughen the surface on the inside and glue some reinforcing material over the back of the crack using epoxy glue.



Mike