You may want to just replace the mouse ball until you get an optical mouse.
This is from a FSB (Field Service Bulletin) I got when I used to work for IBM -
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Abstract: Mouse Balls Available as FRU (Field Replacement Unit)
Mouse balls are now available as FRU. Therefore, if a mouse fails to
operate or should it perform erratically, it may need a ball replacement.
Because of the delicate nature of this procedure, replacement of mouse
balls should only be attempted by properly trained personnel.
Before proceeding, determine the type of mouse balls by examining the
underside of the mouse. Domestic balls will be larger and harder than
foreign balls. Ball removal proceedures differ depanding upon the
manufacturer of the mouse. Foreign balls can be replaced using the
pop-off method. Domestic balls can be replaced using the twist-off
method. Mouse balls are not usually static sensitive. However,
excessive handling can result in sudden discharge.
Upon completion of ball replacement, the mouse can be used immediately.
It is recommended that each replacer have a pair of spare balls for
maintaining optimum customer satisfaction, and that any customer missing
his balls should suspect local personnel of removing these necessary
items.
To re-order, specify one of the following:
P/N 33F8462 - Domestic Mouse Balls
P/N 33F8461 - Foreign Mouse Balls