I had a similar problem with one of my Valeo LED rear clusters. As mentioned, make sure its tightened up as mush as possible. Personally I'd fill the little hole you've made with sealant and seal all around the edge of the glass/plastic where it is attached to the main body of the unit.
If there is room inside the standard light cluster, add a good sized silica gel desiccant pouch and hopefully within a week it will clear all the condensation, then chuck that pouch and replace with a fresh (new one).
Ideally do this on a nice dry, non humid day.
Can be got from eBay. Loads about, here's one ad for some 50g pouches (more than big enough)......
~~ Clicky here ~~MineAdd Silica Gel pouchAfter, now clear