agreed, you need to sort a bleed out for that pipe.. bear in mind the bleed screw on the rad only bleeds the rad itself, its much lower than alot of the water channels in the engine and head, that bleed you have bypassed is on the heater matrix line cause thats the highest part of the system.
Would have been better to pull of the sound deadening and taken the pipes off at the heater matrix itself and joined them together and then you could still bleed - whether thats still possible depends on if you cut the pipes..
Worst case you can just buy something like this http://www.carbuildersolutions.com/uk/black-nylon-16mm-joiner-with-bleed - put it between the 2 pipes you have joined together. But you need to get the bleeder as high as possible - you may need to extend the pipes so you can have the bleeder up at least as high as the original one.
Do this before or the same time as the head gasket
Leak wise, you will just have to search for it to be sure... could try the old dust talc around where it leaks so it leaves trails in the powder. But sounds like its gonna be the metal pipe, its seal or the core plug.
Would have been better to pull of the sound deadening and taken the pipes off at the heater matrix itself and joined them together and then you could still bleed - whether thats still possible depends on if you cut the pipes..
Worst case you can just buy something like this http://www.carbuildersolutions.com/uk/black-nylon-16mm-joiner-with-bleed - put it between the 2 pipes you have joined together. But you need to get the bleeder as high as possible - you may need to extend the pipes so you can have the bleeder up at least as high as the original one.
Do this before or the same time as the head gasket
Leak wise, you will just have to search for it to be sure... could try the old dust talc around where it leaks so it leaves trails in the powder. But sounds like its gonna be the metal pipe, its seal or the core plug.