New formula oil for a Sherman engine

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I received the message below on an email list that Hanno moderates. It is a worthwhile question to repeat here.

"[G104] current oil for GAA engine?‏

Date: 16/11/2013
To: G104 yahoogroups

Gentlemen, We are seeking a current oil substitute for the GAA we are installing in #11965. We are concerned that current oils will eat the sterling silver bearings and if no zinc is in the formula the cam bears will be compromised. These motors have Sterling silver bearings and the oil will pit the bearings.

The oil wholesaler’s technical representative was trying research paraffin based, chlorine free, zinc free current oils but no one has experience with sterling silver bearing pitting. Any suggestion and advise would be appreciated.

Thanks
Russ Morgan