Right click works only sporadically - Wired Mighty Mouse

iMac 4K Retina, OSX El Capitan 10.11.3

Purchased December 2015

(My wired Mighty Mouse came with my iMac at time of purchase from my local Apple Store.)

THE PROBLEM -

When I right click on the mouse when it is set to "secondary button", it only works sporadically, somewhere between 10%-20% of the right clicks. I temporarily set it to something else (like dashboard) and it seemed to work OK for that, although I did not leave it there for more than 10 minutes. I've tried restarting my iMac - problem persists. This problem occurs in all apps.

I think this problem has been happening for me since purchase. I just ignored it for the first few weeks, assuming my right-clicking technique just needed to be honed. When it persisted beyond a few weeks, I got frustrated but still ignored it. After 10-11 weeks now, its persistent, constant recurrence has become intolerable. (Never had this problem with any other mouse on any machine).

Here are the specs for my wired mouse:

Apple Optical USB Mouse:

Product ID: 0x0304

Vendor ID: 0x05ac (Apple Inc.)

Version: 1.10

Speed: Up to 1.5 Mb/sec

Manufacturer: Mitsumi Electric

Location ID: 0x14200000 / 2

Current Available (mA): 1000

Current Required (mA): 100

Extra Operating Current (mA): 0