How To: C15a Wire-3 restoration

[Grant Bowker]

Jordan,
I don't know whether this may be part of the issue or not. M35 and M135 series trucks used a cork seal (wedge shaped) in the keyway/groove highlighted by the arrow in your 3rd picture above. The wedge/insert was claimed to be part of the sealing to keep lubricants where they belonged. The attached diagram lifted from the web is one of the clearest I've seen to date showing where the wedge sits. There are also web posts claiming that a blob of silicone can replace the wedge.

I don't see a reference to the wedge seal in the C15A parts list but I may not have been looking in the right area of the list or might not have recognized what the list called it.... so I'm not sure whether the CMPs used such a seal.
Having said that the seal may be used and might be significant, I don't recall if my C15A has them but I certainly dont recall making them as suggested by many from old valve cover gasket material , or from sheet cork gasket material.