The gearbox is a lot better now. The problem was one of the retaining bolt-spring-ballbearing combinations that engage with the selector shaft.
It is now quite clear that the one involved must not be screwed entirely into the threaded hole but needs to be backed-off somewhat or else it locks the selector shaft solid. I have the feeling that there was supposed to be a washer on it to achieve just this effect... perhaps a washer with a bendable tab that also serves to hold the reverse light cable?
Anyway.. it is all back together. The only slight niggle is a vibration that kicks off when the mainbeam is turned on. This is no doubt coming from some kind of relay box on the passenger side of the engine compartment. I don't know what is causing it .. and it is possible I have dislodged some critical wire. Ideas? Thanks.
Ah yes... I er searched the threads and found that I am probably suffering from a short circuit somewhere in the lighting wiring. I will consult the Haynes for possible problems.
I put tape on the wires when dismantling to indicate where they go... necessary as I am colour blind... but I could have got one mixed up...
There is definitely one left over.. with an eye in the end so it must go somewhere! Everything seems to work though... lol 'cept for the mainbeams!
They come on.. but this damned buzz kicks in so I turn them off immediately!