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It seems the newer synthetic oils work so well, that they actually promote the leakage in the rear main rope seals.
There are a couple oil products that are not a synthetic blend such as Pensoil "High milage", that seem to retard and/or stop leakage after a while.
Any thoughts?

A major advantage of synthetic oils is the extended oil change interval which in my view runs contrary to the type of care that we should give our collector vehicles.

Collector cars are usually driven fewer miles, more frequent multiple but shorter trips etc. which tends to accumulate moisture and combustion byproducts in the motor oil. The best care they can receive in such service conditions is more frequent, not less frequent, oil changes. I change oil in my Packards every Fall regardless of mileage (which is usually about 800 - 1000, sometimes less) and use a good brand of conventional motor oil. Were I using synthetic, I'd be paying considerably extra for a benefit I'd never use and if I did, it would probably be detrimental to engine life if I also extended the change intervals.

Interesting. I use synthetic for the very reason that it does sit a lot. But then, I guess I don't drive my Packard the way in which you've generalized -- fewer miles, multiple shorter trips. I tend to drive it longer distances, giving the contaminates a chance to dissipate.

So West, what oil change interval or regime have you settled on?

I only just started using the synthetic this year, but I thought I'd go 5,000 miles or every two years. If I can ever get a chance to leave my office for a week or so at a time, I'll probably put on 5,000 miles each year. In that case, I may decide to change oil every 10,000 miles.

In the new vehicles the manufacturers now recommend 10K. However, I'm not so sure in the classics. I like the non-synthetics due to the leaking rear seals.
Besides, it's still fun to get under the car like I used to. Now the problem is getting up from down under!

I have the same problem as ALM. It's easier to get down than getting back up. I change oil in November as that is usually
when I put Best Other away for the winter. I do a lot of short trips, but also have been known to drive several hundred miles in a day. If the car show is known to have good food, I might drive a long way Either way, I like to change oil and filter just before I store the car for the winter. I use Shell Rotella and now add ZDDP. It's cheap enough and my car is worth it. Very simple maintenance.
I usually grease the car in the Spring before taking it out.
That also allows for adjusting brakes, etc.

Hi folks:

Since I deal with computer controlled automobiles I figured I would put in my two cents on this.

a) Mobil 1 extended service intervals are contingent on the use of the Mobil 1 extended interval oil filter. However, Mobil 1 is not recommended as a substitute for oil changes with guaratees for 15,000 miles or annual oil changes whichever comes first.

b) Synthetics are great for very high temperatures and extreme low temperatures. They are really good in air cooled motors for this reason. Lawnmowers and motorcycles love Mobil 1.

c) Today's computer controlled engines run almost infinitely cleaner than dirty old carburetors, suction tube crankcase ventilation, and perfunctory air filters so the detergency in the oil lasts longer in modern motors.

d) By the mid-1960's GM was extending service intervals to 6000 to 7500 miles which remains the standard for most motors.

e) Consumer Reports famous New York Taxicab study found that oil changes more frequent than 6000-7500 miles were a waste of money in modern cars regardless of so called "severe service".

f) For a clean occasional use Packard motor using detergent oil annual changes is probably adequate, although in worn motors with lots of blow by the use of non-detergent oil will keep water accumulations separate and therefore less harmful. However, for any Packard motor 3000 miles is probably the limit for detergent oil after which significant sludging will begin. I wouldn't go more than 2000 given how expensive these motors are.

g) I have been told that synthetics seem better for motors that sit because they are more tenacious and less hygroscopic, but I have never examined this myself.

Hope this helps

Okay. Maybe I won't try to eek out more mileage and years from synthetic. Thanks for your input.