I use 20-50 High Mileage Valvoline in my 380sl with 146,000 miles to keep the
seals and gaskets pliable' don't have any leaks or drips. Might be worth a try
for your older 450.
"Life's journey is not to arrive at the grave safely in a well-preserved body,
but rather to skid in sideways, drink in one hand, totally worn out, shouting
"...holy shit...what a ride!"