Hi All,
Adrian - Don't know about that, Pavel has just enlightened me on something I thought I knew

As for photo's, I always seem to forget the camera until too late - will try to remember.
NZMark & Robert - hadn't heard of pepper but can see the logic, sawdust, cornflour, ground oatmeal and egg all seem to have been staples and another which I used on my Industrial Standard was mustard powder (this was my first tractor back in my teens) ran around with the mag set so she was pinking, got good and hot and the leak slowed to a dribble, put her on the saw bench for an hour or so and despite the yellow streaks no water seen THEN I made my big mistake, I undid the filler cover and breathed in just as the pressure released in my direction

the tears took a day to stop, what my kids call brain freeze (the sensation when you eat ice cream too quickly) took several days to depart OUCH mustard should come with a health warning
Pavel, thanks for that vital bit of info on the silver solder use, having seen modern rad production video on the TV I had assumed the tubes were float soldered into the endplates like they do PCB's with soft solder, thats obviously something more recent for cheap and nasty production, on the upside is the tube joints will be a lot more substantial so less likely to have suffered frost heave than the header joints and if leaking there, it is OK to soft solder caulk over silver solder (the reverse is not the case as I have found when people have brought me small steam boilers they have failed to soft solder when they should have hard soldered or brazed - something about the lead content)
As a useful tip in return for all yours, if you are either soft or hard soldering using a torch for heat and don't want solder flowing wherever the flux runs when it warms, draw around the joint with either a soft pencil (I tend to use the carpenters sort) or paint round it using Tippex or similar typists white correction fluid (getting rarer with the demise of the typewriter of course !) both resist the heat and neither solder type will bridge, I used Pencil when I soldered the bottom of my fuel tank which left quite a neat magin and allowed the solder to pool more thickly than it would otherwise do (also handy if trying to repair a PCB where solder insists on running, likewise if replacing a component and the solder sticks in the 'ole and refuses to blow out, poke a sharp pencil in the 'ole while the solder is wet)
I'll let you know how clogging up with foreign substances in the water works out but it'll only be temporary (currently favouring a 'batter' of soap, cornflour and fine sawdust)