I replaced the heater core on my 1987 Toyota pickup with a replacement heater core from Napa and its aluminum
My problem is one of my tubes that connect too the core is bent or tweaked and when I attach the inlet and outlet lines
the tube on the right side of the core, the outlet tube moves or shifts and the retaining clip moves and the tube separates and leaks
I have unassembled and reassembled the dash and the core twice and it has separated twice

I found this picture of using 2 different sizes of heater hose and hose clamps

And wondering if it would work to keep the retainer clips and the tubes in place ??

another option would be to find a original copper heater core and silver soldered the tubes and core together

Cause I can not find replacement tubes or a copper heater core but still looking for one

 

This is what it has done twice and trying to avoid a third time, it separates and leaks