Q: optical A1296 mouse scroll problems

I have had my A1296 optical mouse without problem for over 5 years now.  All functions work fine except for scroll down.

Several posts referring to cleaning detail roll ball problems but opticals don't have roll balls.  Also my screen will zoom in and out

erratically without my control. I've gently cleaned optical eye with 99% alcohol.  Do I need to buy a new mouse or can I salvage?

27" iMac mid 2011

2.7 ghz i5

vers. 10.11.4