I add half a dozen o-rings (from memory I think they are BS010); hole is drilled out to 3/8", and approx 2/3 of the depth of the outer thread.
This has stopped the leak in every A10 I have done it to; no shrink wrap required.
I also machine a groove on the OD of the brass speedo drive carrier.
I see on Lyford Classic Services web site, they supply new brass carriers, with the O-ring groove already provided. I suspect they have also modified the bore, to take the o-ring for the speedo gear shaft.
Richard