The gasket used was a non-lockstrip unit, though I can't remember if it was an OEM gasket or not. I've had no issues with water ingress from it that I can see; just the drip from my rear view mirror during turns in rainy weather, which I think comes from failed (factory) gutter sealant in my A...
If you have wiring running up your A pillar "underneath" your headliner to an aftermarket powered mirror, taking a turn can let water that's coming in through the A pillar travel along the wire and drip from the mirror as well, so if you're seeing water dripping from your mirror, this is another...