If you can pin down the exact location of the leak that seems to be present as a result of the carb cleaner test, then you could try a quick and dirty fix: use silicone sealant on the leak. Clean the surfaces the best you can and apply the sealant. Since there is vacuum and not pressure inside the manifold, it will probably remain in place (did this with a 240 once - lasted many months until I finally replaced the gasket).

To help pin down the location, you can also use a piece of rubber/plastic tubing. Use it as a stethescope and probe around the idling engine.
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'61 122s B16, '67 122s B18, '76 245 B21F, '81 245 B23E, '90 745 B234, '95 960 B6304 (not counting parts cars)