The monomer density reequilibration relaxation is directly observed for the first time from the linear viscoelastic data of very high molecular weight linear polybutadiene, polyisobutene and polyisoprene. We use a simple procedure of subtracting contributions of the high-frequency Rouse-like modes from the experimental curves. The stress decay of the monomer redistribution process is characterized by a single exponential (Maxwell form), and the observed relaxation strength is one-fourth of the plateau modulus. Moreover, the characteristic relaxation time is close to the equilibration time tau(e) of an entanglement segment. The observed reequilibration dynamics appears to be independent of polymer species. The high-frequency relaxation modes can be reconstructed as a superposition of power law Rouse-like dynamics and Maxwell monomer reequilibration. The dynamic moduli curves calculated in this way show excellent agreement with the experimental results in the high-frequency region. We further propose a possible "experimental definition" for tau(e). It corresponds to an easily observable cross-point between the extended plateau modulus and the power law region of the loss modulus.