Marvel oil has been around for a lot of years so it can't be totally worthless & still be available. Whether it would solve anything for your car down the road is a question. You said you didn't drive the car often but one of the supposed benefits was upper cylinder lube and valve stem lube to help prevent rust and sticking in dormant cars.
Had left a post yesterday re the possibility of finding an old period correct automatic dispensing system for the Mystery Oil. Later on decided not to arouse angst & deleted it. Now that someone else has also mentioned mystery oil as a possibility, then it might still be a viable idea. Some of the old original units are shown on this post
https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=4884&viewmode=flat&order=ASC&type=&mode=0&start=0 and show up on ebay fairly often.
If you decided to try one, doubt anyone could call it terribly wrong since Packard dealers were known to sell and install them. Might have been a fad of the time as many other things were -- though modern versions were still available as of last year. In any case, if you had an old one it certainly would be a conversation starter if any of the younger people saw one and asked what it was.
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