The exact two-potential description of the dynamics of the liquid outer core (OC) is solved numerically, using a Galerkin method, for a rotating spherical earth model (original and modified PREM). Coriolis effects are taken fully into account in the OC. Deformation of the inner core and mantle, incorporating Coriolis self-coupling, is included via internal load Love numbers. Special attention is given to conditions at the geocentre in computing Love numbers at the inner core boundary (ICB). Internal undertone oscillation eigenperiods are computed for PREM modified to have a uniformly stable OC. For those modes involving no significant degree-1 spheroidal field, the assumption of rigid OC boundaries leads to smaller errors than adopting the subseismic approximation. Slichter mode eigenperiods are computed for PREM and for PREM modified to have a uniformly stable or unstable OC. The stability structure of the OC has little effect on Slichter eigenperiods, which are almost inversely proportional to the square root of the ICB density jump for earth models with the OC so modified. The effects of ellipticity and rotational potential on the Slichter eigenperiods are estimated using perturbation theory, and the effects of melting/freezing at the ICB during a Slichter oscillation are shown to be negligible.