Water ingress. I had noticed water getting into the boot now and again and it became really apparent whilst working on the top shock absorber mount last week (see photo from last week). I think the problem was that the previous owner had had a CB aerial mounted on the rear deck in the past and the grommets he used to plug the hole didn't do a good enough job - see above. Doesn't look great does it? Over next winter I aim to have some bodywork done and this will be fixed then but was there something I could do before then?