Does anyone have the part number or where to order the T-176 /Dana 300 adapter plate gasket and oil seal? I don't show it in any of the catalogs but find it online with master rebuild kits.
If you have the old seal out you should be able to take it to a bearing supply and they will pull one from the shelf based on size and mfg #.
The gasket can be replaced with locktite 515 gasket eliminator or a piece of gasket paper and a few minutes with a ball peen and an Exacto knife.
At least that would be what I would do if this became more than a minor problem to find.