It seems that the lens go quite brittle over time for most people, so is there anything you could coat them with to strengthen them and prevent cracking?

 

You won't be able to prevent it entirely. The plastic's chemistry is what eventually cause the taillights to crack. Intense heat and UV will degrade the plastic and it will craze, and be more prone to crack. If you're still keen on it, you could coat them in a 2 part clear epoxy to give a layer of protection. However, that doesn't reverse any damage which has been done. If you want new looking taillights, get a new set or find the cleanest set you can.

 

Yeah I bought some of this. It's quite expensive but apparently it has a refractive index similar to glass and takes 10 years to begin to even slightly yellow from the sun.
https://au.element14.com/araldite/ar...5kg/dp/1759533

 

I couldn't find where it makes the claim of not yellowing for 10 years. But more power to you if it does what you want, let us know how it turns out.

 

it's on the middle of page 4 here http://www.lindberg-lund.fi/files/Te...N-XW396-TD.pdf