thank you. This is great info. Hopefully, the leak down test will be conclusive.3 cylinders with no compression?
Time for a leakdown test. If you've got leakage past the valve(s), you'd need to verify lifter preload, and if that's good...the engine needs the heads removed for valve work AT MINIMUM.
If the leakage is past the rings--or holes in the pistons--the engine is pretty-much "done" and needs a proper rebuild.
And if the leakage is from one cylinder to another, you can HOPE that a new head gasket will fix it.