After “The Alamo” sculpture, known by most as “The Cube,” was removed from Astor Pl. by the Parks Department for repairs earlier this month, some art students — in the spirit of public art — erected a temporary replacement on the site made of PVC tubes held together with light packing tape. The replacement “Cube” was flimsy, but it remained intact for a few weeks, until last weekend, that is, when somehow it was knocked apart. “The Alamo” needed repairs to its base, which had become unstable, making it impossible for the spinnable cube sculpture to move anymore. Parks said the sculpture would be fixed and returned in about two months.