Not very easy to see here but this is the remains of the weeping core plug - not very much left. I had had quite a problem getting a replacement as all the suppliers had this item as "no longer available" but it seemed ridiculous for a £1 component to be the cause of such grief.
Bryce decided to buy a ouple of boxes of assorted core plugs as they will always come in handy so we felt confident we would be able to sort this one out.
Like may occasions, however, it didn't work out as straight forward as expected. The old core plug decided to make a fight of it, so much so that we took the bonnet off (!) to get at the core it. It was then much more simple to get in and tap it out.
It was then that we found the core plug required is a very odd size indeed and wasn't in ether the metric or imperial assorted core plugs Bryce had bought! Much hunting round and head scratching came up with an answer which was to thread the inlet manifold, screw into that an adaptor with loctite applied and screw into that a "sump plug" for want of a better word. Job sorted after which it was just a case of refitting the bonnet etc.
The solution can be seen in the photo below.
Once again a job that should have taken 40 minutes actually took much longer, 2 1/2 hours in fact!