So i noticed condensation inside the indicator lens of the indicator mounted in the wheel arch. Decided to replace it with brand new genuine and its doing it too! Its a sealed unit, so go figure! Even more weird is that the other side doesnt do it...

maybe the rubber seal where the light mounts into lens is worn out?

maybe the rubber seal where the light mounts into lens is worn out?
There is no seal from what i remember. They just clip into place. I'll have another look to try and understand it.

Any splash guards missing from under the engine?
Water drain for the plenum chamber blocked on that side?

I have one in front of me, definitely has a rubber seal on the light bulb fitting itself. Light bulb fitting twist turns into lens. Maybe get a new o ring to suit will fix your problem , unless lense itself is not sealing properly but as you say it is new so shouldn't be the problem.

from my memory the case can crack and allow moisture in? I had one replaced under wty, it lasted a few years then had the same problem. I was told it was a common problem, I've never taken it out to have a real close look at it.

I would go for the simple things first. Rubber seal on light fitting is a simple fix. I have two tl's with no problems with leaking indicator lenses and they look original. Easy to remove.......