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The joint detection of gravitational waves and light from the binary neutron star merger GW170817 has ushered in a new era of discovery. HST has played a pivotal role in characterizing the optical and near-infrared (NIR) evolution of GW170817 comma with reported detections of the kilonova and afterglow spanning virgul10-350 days post-merger. In particular comma at >100 days comma the afterglow brightness is extremely faint at >26 mag thus all detections or constraining upper limits at late times were enabled by HST. One major complication in measuring accurate photometry of the faint optical and NIR afterglow is contaminating light from the host galaxy comma which has complex morphological structure. The only way to properly address this issue is by re-visiting the field after the afterglow has faded to obtain deep multi-band template images comma against which we can subtract earlier epochs. Motivated by a case study in one of the optical filters comma here we propose 13 orbits of HST-WFC3 imaging to obtain late-time template images in four filters comma comprising all filters which have HST imaging beyond virgul100 days and for which no adequate template images exist. These images will enable reliable and uniform photometry of the optical-NIR afterglow to GW170817 for the first time. In conjunction with ongoing radio and X-ray campaigns by the community comma this will allow accurate inferred properties of relativistic outflows from the merger comma and the deepest limits on a star cluster at the merger position comma strongly constraining the binary progenitor.s formation. Given the high-impact nature of GW170817 comma we waive all proprietary rights associated with data from this proposal.