I think the substance you mentioned is probably a grease-like anti-scuffing compund which is applied to cam lobes, tappet rubbing faces, lifter faces, and even crankshaft thrust bearings. It is a bit thinner than normal grease and kinda "sticky". It is useful during the 'bedding-in' phase of reconditioned parts and allows surfaces which rub together to bed in with less frictional contact and consequently less risk of damage from galling, siezing, etc (should not be used on bearings though. Use engine oil on those areas). Usually comes in a small bottle or tube and any place which sells engine parts should have it. One small container of it should be enough to do quite a few engines. Often known as "camshaft and lifter pre-lube".
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