The header tank cap that has the pressure relief spring in it was tested when the new coolant system was fitted and was working fine.
Mine is also still on its original plastic tank. So 28 years, have never had to top up the water outside of coolant changes..!
yes, I gather this from your written description but I can't make this out in the picture and that's why I replied.
Sounds a good idea, as I posted earlier I have an alloy tank that I bought years ago after a spate of failures. Mine has no sight glass or any means of knowing the level but it's been fine, I just make sure it's full and any overflow will go to the catch tank. Not as pretty/sculpted as Proalloys (though you can't see it anyway) but well made and strong enough to never fail, not had any problems. That said, you'd think the sight glass should hold so, maybe just unlucky and a new glass will cure it?
