Could try this : [https://electronics.stackexchange.com/questions/343863/how-do-i-clean-repair-a-rotary-encoder](https://electronics.stackexchange.com/questions/343863/how-do-i-clean-repair-a-rotary-encoder)

Also not sure if lubricant is an option if that fails. You sound fairly picky about this specifically so I would consider just ordering a bunch of different ones and trying them till you find one you like. I personally really like the G Pro (wired) encoder, but I'm not sure what the precise model is . 

My G403 has fairly damaged scrollwheel despite only a few months of use (loose steps, scratchy sound), any suggestions for a good encoder that has distinctive steps but isn't stiff? (The one on the GPW is awful). One I can get on Aliexpress/ebay and preferable lasts a bit longer than a few months.  
I want to repair it to at least get it back to a an acceptable state, I already RMA'd it but Logitech gave me a G603 instead, which also developed wheel issues and im on my 2nd G603 now.

Need new Rotary Encoder for G403.