I plan on using Rotilla in our 300 once I get it going. I don't think I'll bother with synthetic year-round, but I am thinking about switching to it from Nov-Feb for better old weather performance. I was talking with a guy who had done some automotive engineering work that included a lot of oil analysis, and as a result of what he said I'm tempted to try Mobil 1 synthetic in some of our gassers that get a lot of miles put on them.
I still haven't quite decided whether the price-performance ratio really works out on synthetic though.

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Once and future king:
'64 Ford Fairlane w/approx 238,000 - looks rough, but amazingly reliable if you know how to look after it; I will soon begin work to totally restore and modernize it.
Family vehicles that I lay some claim to:
'78 300D w/approx 350,000 original, '62 Ford F100 4x4, '90 Ford E150 w/171,000 original