On the very coldest nites several small leaks have developed on my 300D as well. In a couple of instances the clamp in the area was tightened a tiny bit. In a couple of cases when it got markedly warmer the leaks disappeared. Suspect it is mostly related to much lower than usual temps and hoses that could be a little on the aged side.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150