I have what appears to be a slowly developing tiny rack on the dashboard's passenger side. See the picture below.

I noticed some early signs about a year ago. It is not opened up yet, but I think it is extending (in length) slowly.

Any ways to fix this crack and prevent from further expanding (in length and width)?

 

cheap plastic!

 

In aviation and possibly some other industries, there is a technique called "stop drilling". basically you arrest the crack with a man made hole such that it stops the crack with a round hole.
See pic. Create a drilled hole, not too big, at the very end of the crack line. From there the crack will not continue. You can then fill the hole with your favorite black filler. The hole you drill should be slightly bigger than the crack width.

 

Get a fresh coat ceramic coating on it, and tint the windshield with the lightest tint possible. All of my cars have crystalline tint on the windshield. Some will say its illegal and that you shouldnt, but I live in LA and every celebrity I know has tinted windshields. So do all new Tesla cars.

 

Celebrities may do lots of things, but they certainly are not setting a standard for me.

 

A bespoke gentleman driving a Jaaaaaag sets the higher standard. I suggest tinting everything as well.

 

love you guys,, XJS forever!

wide body rear

 

I live in Louisiana, every moron I know here has tinted glass. Moron's Handbook

 

all my cars,except XJS has tint, HEY Texas and Florida , yah gotta have tint!
ron

 

No tint here. Love that old slightly green-tinted glass. I think recovering in leather would be nice. Stitched seam at instruments.

 

The original question was how to prevent it from getting worse. Leaving it alone, or recovering it is what the OP prolly doesn’t want to do. So ceramic coat the dash and dont tint. But at least protecting it via a good coating is an option. Tint or no tint thats your choice.