So, I went to start up my Macintosh Plus for the first time in a while and the system itself was fine. However, when I went to use the mouse I could only move the cursor horizontally, not vertically. I opened up the mouse, nothing blocking the sensors and everything was clean. 

Does anyone know how to fix this problem or where I can pick up another M0100 mouse for a reasonable price (I live in the UK) since the ebay prices are ridiculous.

-Thanks.