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From personal experience don't bother. When i bought my car the headlight lenses had been removed so as halo's could be installed. After the car had sat out in some cold wet weather condensation made its way into the lenses and got to a stage where there was so much water in there the OEM ballasts got corrosion due to water ingress and lead to my headlights not working which was a massive ball ache.

I managed to remove both units and change components which didn't solve the issue therefore it was a wiring issue within the headlight and ended up buying new headlights.

This is the hack job that i had to deal with when i took it upon myself to try fix the issue and dry the units out.
Although i resealed both lenses to the headlights with BUTYL as mentioned above this just didn't give it that OEM factory seal as before mainly due to how these headlights built and how they seal so then water still made its way back into the headlights causing even more damage.

I would strongly recommend ditching the replacement lenses as i to looked at purchasing these and just buy new units. I understand they are expensive however its the right thing to do to ensure all components are dry and sealed off away from the elements.

But that’s because you’re dealing with someone else’s work? Or do you think once they’ve been split that’s it. They’re compromised?

I know a few people who have issues with non-split lights. Not sure but it’s probably to do with the rear covers? And them not sealing again as the rubber ages? There isn’t any other way water can get in... the OEM bond between the headlight plastic and the lense is pretty strong!