As I have removed the unit in order to replace the spigot shaft bearing (amongst other things) I decided that some kind of overhaul was probably necessary.
The symptoms are present when in neutral with the engine running, disappearing when the clutch is depressed. Input shaft bearing I hear you cry!

The gearbox is otherwise well mannered and very good, so I didn't want to swap it for one of the two second hand "spare" boxes I have, condition un-known. I have done a fair bit of gearbox work before so even after I had read the Haynes manual and the Bentley manual I was not phased. I resigned myself to dismantle on of the spare gearboxe first and to get the bearing numbers from this, also to use this as a bit of a practice. The problem is that the bearings are practically impossible to get, it would seam. Though Aidan Talbot does list them on his web site. A set of bearings is a fair step of money.
I have now found myself reasoning thus:
Could at least some of the noise have been caused by the almost none existent spigot shaft bearing?
Having removed the bell housing and gear-change housing and inspected the parts there in as closely as possible I find nothing mechanically deficient.
I know from experience that noisy bearings can be noisy bearing for a very long time and need not be anything to worry about. On the other hand I also know that they can also let go at any time without any warning. Having said that so can one that is making no noise!!
I figured that the parts, seals, bearing, gaskets etc. were likely to cost somewhere in the region of £280, judging by the prices Mr. Talbot has mentioned on this forum. I could spend this money and then make an a*** of doing the job myself, quite possibly!!
So what I need to do is nurse my existing gearbox until such a time as I can afford the services of the afore mentioned Mr. Talbot.
To this ends I have done some internet research, and discovered something called Lucas Heavy Duty Oil stabilizer. The claims made for this product are astounding. Does anyone here have any experience of this product? Is it something which is worth a try or something to steer well clear of. It claims not to be the usual slick 50 PTFE block all the oil ways up type of stuff...........
One other thing of course is, I assume that my gearbox is making a noise, but, I have nothing to compare it with, it has made this noise for the last5 years (since I had it) perhaps I'm expecting too much of it??
Andy