how fix clicking lifters?

I have a 1991 350SDL with clicking lifters. I assume the oil channels could be blocked to the lifters so the oil pressure isn't sufficient. Someone recommended an engine flush to dissolve the carbon in the oil channels or tubes. There seems to be some debate about that idea. If that isn't a good idea, how do you get the click out?

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Stan Rodbell
91 350SDl
83 240D