FWIW, I've just been looking at the records available to the public on the Cosford website. It records that 818 went to 32 MU at Hurn on 16 Jul 61 for modifications to a tanker., although several flights are recorded after this, until 28 Sep 62, when it was returned to 49 Sqn. If anyone wants to read what Cosford has, here is the link.
https://www.rafmuseum.org.uk/documen...iant-XD818.pdf