What I'm I looking at time wise to replace it. Is it worth it to try k-seal or am I asking for bigger problems. I know I can replace it. But it's getting cold and the heater core just went out.

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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800