How should steal seal head gasket repair be used, does it work?

my car - 2006 ford focus 1.8 tdci. It s had around £2000 of repairs in under 2 years of my ownership

Car had chemical test 15 months ago, indicating bad head gasket.
however 15 months on no symptoms of hg failure, no water/oil mixing, no power loss, no smoke, just have to top water up every week or so.

I would replace hg but car has other problems so don t consider getting it done though I am constantly debating it.

anyway, this steal seal says pour in radiator but my car has no radiator cap, so would I just need to pour it into the coolant header tank? Is steel seal an y good?

thanks

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