Well, currently 242 viewings of my post and nobody is none the wiser.

So I emailed the Manx Museum today, and got a prompt response

Many thanks for your email which has reached me. The story with the clock is as follows. When the scoreboard was taken down MNH was given the opportunity to take the pieces that we felt we could use. At the time we asked what was happening with the clock. As the staff at the Motorsport office did not have an immediate use for it, we offered to take it on a loan basis to keep it safe. We had it for about a year but after that the Motorsport office asked if we could return it, which we did. I’m not sure what the reason was.

If you will allow me to pass on your email address, I will try asking some contacts there what the plans are for the clock?

I have thanked the Museum for their response and asked if they can pass on my email.

Will see how it goes, but the mystery continues