You can also simply go back to the tar rope old school type as well, car will never know the difference. You'll need to cobble up edge bumpers to do so. I simply used short pieces of fuel line when I did mine.

I have used black "Shoe Goo."  It seems to bond to rubber (and glass) well. I sanded the old rubber to remove the dry, crusty layer and give it some "tooth."  Mask off where you don't want it to go.   Rub it into the crack ends, then fill the crack.

 Don't use it out in the sunlight on a hot day. It sets up pretty fast.  You need to move fast with the stuff.  I recall letting it self level.  I did the lower portion so I can't attest to how well it works on the sides or top.  Also pull the tape as soon as you are content with the application. Shoe Goo isn't like paint. Note the picture isn't a Pinto, it is my '64 Daytona (Studebaker).  There was a 1/2" gap about 12" to the left of the corner. It filled and blended well. I then "topcoated" the rest because it was filled with small cracks and irregularities . The end finish is more of a semi gloss than a flat black like a regular gasket.

Thanks I think I'm going to try Shoe Goo for a temporary fix I have some rust spots that I probably should fix that are around the windshield rubber I'll probably need to order a couple tubes because the cracks in the rubber are the size of the Grand Canyon

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I was thinking of the exact same thing for one of my Novas, don't have time to put a new one in right now and I hate for water to get in there and start rusting.