Valve seals leaking? Very common on oldergm v8 and 6's. Another method of cleaning out a block is to drain the oil and refill with atf and a couple qts of engine oil. Warm the engine up,run it for a couple blocks, and drain the oil. Do the filter too. Atf has a high detergent agent in it and works well for cleaning out the engine. The nice thing is that it is safe to drivefor a short time.used this method lots in in the past and is real effective in cleaning up hydraulic lifters.however if doing this and the solvent treatment doesn't work then the rings are done and that's it.! I'm not discrediting the solvent treatment....never tried it as the atf worked so wellong for me. Also have seen but never used is a additive for engine oil that works the same as atf,I don't recall what it is called.
