Just a quick update. Sadly, I am still no closer to finding it. The situation is that I have now been in contact with the person who sold it back in 1995. However, they claim to “not remember that time” which is odd because, even though it was 28 years ago, it will have been the only occasion in their life that they have sold a guitar, so its extraordinary that they can’t remember a single detail about it. I've sent a follow up with more questions but have yet to receive a reply.
In the meantime, there are threads running on all the major Facebook Rickenbacker groups, in both of the dedicated online Ricky forums and other bass related sites like this one and alerts are set up on Reverb and Ebay. I guess its going to be a waiting game now, not sure what else to do, but while I think about that, here’s more pics.