Other than replacing the entire dash, what product can be used to fill and stop the crack from extending? OK, it won't look perfect, but is there anything decent?

Mine has one crack at each speaker.

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI