The EGS also had a torsion bar suspension. According to cross sectional drawings, there are two elastomer mounting elements: one around the support bearings, which connect the running gear module to the hull and one around the torsion bar, acting as air-tight seal. Unfortunately I am not sure if this is the correct translation of the German terms.
Here is a image from a patent showing a vehicle with a decoupled running gear (and diesel-electic drive). The elastomer connection is marked as 10. On the drawings of the EGS suspension, there is another elastomer connection/seal at the torsion bar. I suspect the M113 might have a similar system.