Commiserations. My first PB160 was also defunct horizontally. Removal of the trackball assembly (661-1515), cleaning, cossetting and swearing was to no avail. It was six years until another (NOS) appeared on eBay, for USD0.99 purchase and USD20.00 for shipping. The PB goes like a bewdy with its new trackball assembly, and the temporary loan from a PB180 was restored to its prior home. Good luck to you, anyway. You need a 661-0730, which also fits a the PB160 and friends.

de