The main culprit was the fitting that I made up several years ago when the M50 was installed to mount the switch for the electric fan...

There was a pinhole in my weld,that rusted bigger,I removed the fitting,re-welded,examined my weld,checked the welder settings,ground back and re-welded again with the gas turned on
This cured,or at least improved the leak,but the thing was still running too hot at sustained engine speeds above 3000rpm,so I came to the conclusion that I had a circulation problem.Both waterpump and 'stat were new not long after the engine went in,so I started to suspect the radiator.
I fitted an ex-M40 rad that I had 'in stock',mainly because this offered the correct fitting for the fan switch,this completely cured the leak,but still gave me the high speed issues,so I concluded that the elderly ex-M40 rad was probably silted up like the original.
Emailed meatballs82 at ECP and asked for a quote on an air/con type E34 radiator,had a reply within 10 minutes with a link to a high res photo to check suitability,confirmed that this was OK and received a very competitive quote,I'd already phoned my local GSF to discover that they would need two or three days to obtain the same rad,for same day dispatch.
Radiator arrived before midday the next day(Friday,yesterday)in perfect condition.

From L to R above,M40,E34(from my engine donor)new radiator.
As you can see,the new rad is significantly taller,but the extra hieght is all below the lower mounting points,so it fits into the void just above the front undertray.

Matt's service from ECP included a follow-up email om Friday to confirm safe arrival,in all,the service received was way beyond first class,this guy will obtain more business from me...quality is remembered long after cost is forgotton...
Meatballs for PM!













