Has anyone used those Chinese aluminium radiators that are on eBay?

So drove to work this morning after topping up the radiator again. I only use concentrated coolant and demineralised water. Park it up and a couple of drips on the concrete. Let it cool for 10 mins and opened the cap with towel of cause. No fluid loss. Then revved it up and fluid goes down slightly and back up when left to idle with no real bubbles to be seen. Watched for five minutes and put cap back on. Couple of dribbles start again. Then I turned it off and the dribbles or drops then turn into a constant flow out the overflow pipe but only happens when you turn car off. Pissing me off at the moment.

that sounds exactly what my fairlane was doing  thought it was the head gasket on its way out or cracked alloy head ... car was fine driving.... and cap off didnt do anything  abnormal but as soon as i turnned engine off  within couple minutes it was pissing out of overflow
 
after little bit of searching and doubble checking was the radiator cap seal and wrong radiator cap
psi rating ... the pressure was pushing the spring up to easy and would piss out of the over flow.. went and got one of a spare radiator and never did it again
 
just check that the seal is good and fits in the mouth of radiator fully  some sit flat and seal.. some i notice made in china crap  dont sit flush and only a portion of the seal is  sealing so wont take much pressure to spring it up or one side and then you get the overflow pissing out
 
 

Based on what I have read there is no way you need to pull the heads off and you should avoid that like the plague.  Every skim changes how the inlet manifold lines up and seals because of the V shape and soon you get to the point where front and rear manifold seals fail.  
 
My guess is that the little raised ring that the cap rubber seats on is corroded and letting water past - it happened to mine.  You don't need to worry about priming with the heater on, the heater controls only move an air flap, there isn't a valve in the water system like on modern cars.  Slow bubbles could just be some cavitation in the pump.  If you had anything more sinister you would have a stream on bubbles and the pressure test wouldn't hold.  These things are hopeless in traffic on hot days so if it is corrosion on the cap seat get a new radiator custom made with more cores and fit a recovery system, there's a good reason why every modern car has one (A recovery cap without the bottle does nothing different to a normal cap), and while the radiator is out you might as well fit a new pump to save you doing it all again later.

I bought another new cap yesterday and will try that. The radiator does seem to be in great condition so I will pull that out and flush it as well as the whole system. The Perana radiator was $100 to get flushed and braze welded at the cap fitting and almost spent that now on new caps and coolant. Let you all know how it goes in a couple of days. I do have a new water pump as well for another car but will install that at the same time. Thank you for your advise.