The two bathroom washbasins in this house are different. Both are set into tiled countertops. One rests on a rubber (?) gasket. The other has no gasket, and appears to have lifted 1 mm. at one edge; water leaks into the cupboard underneath (creeping round the lifted edge of the basin? The basin with the gasket has noo such leaks.)
Is it feasible to reinstal this washbasin, simply by unfastening the retaiiners (if not too rusty) and inserting a gasket? Should this be a premoulded rubber gasket or a bead of caulk?