Hi, So I did a leak down test on the head of my W115 and 5 out of the valve's failed and held no liquid.... so since I've never done this job before, and I haven't done this type of thing for a long time now... do I need to replace the valve seats or valve seals?? I have a box of new valve seals.... they are rubber sort of things with a spring stretched around them, so new valve seals or seats to make the leak down test a success....

Thanks J

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1975 240D W115 version 3 (Australian car )