In article . com,
"Jay Honeck" wrote:

I agree, it's a cool plane. The coldest I've ever been in my life was
flying a 310 into Rochester, MN....but I digress...

Probably worn out door seals.
I flew right seat with a friend from Ohio to Florida and back one trip.
I could feel the draft when the seal lost pressure. There was a hand
bulb air pump that would squeeze until I felt resistance to indicate the
seal was pumped up. No more cold air draft.