My driver's door armrest cracked which I read is a common issue.
I fixed it with a part # 420 Bondo Fiberglass repair kit availalbe from any auto parts store and some big box stores. Get disposable gloves too.



There is a good YouTube video on door panel removal. https://www.youtube.com/watch?v=xuJJ...el=DIY:CarModz

First pull off the foam insert that is in the way.


Then sand the patch area with 80 grit sandpaper so the area is rough enough for the fiberglass to stick.
When done, push the cracked areas back into position. Feel it from the upholstery side to make sure it is smooth.


Cut 2 pieces of fiberglass cloth big enough to cover the entire weak area.
The kit has enough material to repair all 4 armrests if you want.
You'll want disposable gloves from here on.

Tip: when mixing the epoxy, put the liquid resin on one end of the tub and the hardener near the other end. Then use the supplied spatula to mix it. DO NOT put hardener right on top of the resin or you will have an epoxy "booger" in your mix.

Work quickly to coat the area.
Soak the first layer of fiberglass in the tub and apply it.
Coat the applied fiberglass if needed.
If you run out of epoxy mix, just make more.
Soak the second layer of fiberglass in the tub and apply it.
Coat the second layer with epoxy.
Let harden for a few hours.


Fixed mine a month ago and it's rock solid.

 

Nice, thanks for the tip.
Mine is broken.
Future project...