We bought ours (a 1070+) in August 2015. We quickly noticed some strange light "spots" in the image, but since at the time it did not affect the viewing pleasure that much we wrote it off as something else.
Then, over the winter we completey rearranged our home theater and didn't use the projector for about a month. The projector was relocated and since we now had a much bigger screen we had to recalibrate/refocus it and that's when we saw it, fiddling around with the zoom and focus: dust all over the lens. We lived with it for a few months but by August 2016 it was so bad that when in focus it looked exactly like looking up in the sky on a starry night, and it was very noticable in light and dark scenes.
We had it fixed by BenQ (took a friggin' month!) and it came back free of dust, and - according to Benq - "sealed" so it couldn't happen again. Yeah right ... less than two months later we began to see dust again and now four months later it's almost as bad as it was before repair.
I guess we will give BenQ one more chance to fix this, but have to admit I'm deeply dissapointed in the quality of the 1070+ lens engine sealing!
Benq W2000 (HT3050) // 130" DIY screen // Pioneer VSX-AX2AV (7.1) // Infinity Beta 50/C360/ES250/Mission 737R/Dynavoice Thunder T-12 // Samsung BD-J7500 // PS3