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I don't mean to question your experience or technique so if my post does not apply please ignore. The declining compression pressures may be related to cranking rpm if you sequenced 1 2 3 4. Perhaps 4 3 2 1 with a fresh battery would change or support your existing readings. An accurate compression reading can be obtained with a fully charged battery connected to a battery charger. After one cylinder has been tested wait until the amps drop on the charger and check all cylinders at the same amp reading. On the #4 cylinder, put a plug in from one of the other cylinders that you know is firing good. Run the engine, note the rpm, pull the plug wire and hold the terminal about ¼” from the plug. That will introduce an auxiliary gap that retards the coil discharge producing a higher voltage spark. If the engine rpm picks up there probably is excessive oil in the combustion mix. A wet check is good for worn rings but it doesn’t mean much if a ring is broken or the cylinder is scored. I think I would drop the pan, and check for ring pieces and try to view the bores and piston skirts. Of course, if you find something here an overhaul is in order. At least you know what you’re getting into with less effort. Joe
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