Taking a punt on these off aliexpress...
I have no idea if they are genuine. but they have sold many of them and reviews speak positively.
This is mainly for my Logitech G502 spectrum which has developed the double clicking issue that plagues a lot of Logi mice and rendered it basically unusable now. Decided to order 4 pieces as I think my old G900 will eventually suffer the same issue. The sensor in both these mice should be the Pixart PMW3366 which are quoted to be better than the newer 16k and 25k Hero sensors that are used in the current gen of Logi mice.
If this works. it would have cost me under £10 total to fix. I already have a soldering iron and soldering something like these is easy. I would have liked a new and fancy Logitech G G502 X but no way in hell im paying over £70 for one. Not when I can fix this old 502 for under £10. The G900 will cost a little more as I also plan to replace the battery inside as well which i think is getting a bit long in the tooth now. Purchased it in Dec 2016!
::EDIT::
My fancy bicycle wheels are almost here... Its been OVER A MONTH (ordered on the 20th last month. TWO WEEK lead time....) but it should be here within the next week.