355 Leakdown Test question

If they ran rich they wouldn't pass smog and make enough exhaust heat to destroy exhaust manifolds. In fact they run very lean.

If there are excess deposits on the back of the valves the guides are bad.

 

Leaking from intake valves is typically either debris in the spark plug well or deposits on the end of the plug fell onto the intake valve face and caused a false failure of the test. It should be SOP to blow out the plug wells with compressed air, loosen then retighten the plugs, restart the engine briefly then do the test.

The only other reason it should be leaking from the intake is if cams got out of time and bent valves.

 

Is this more around-town but WOT AFR's are good, or are they lean at WOT as well?

 

No such thing as a rich mixture under any condition on a car built in the 90's. What do you define as good? The leaner the better right up until engine parts melt. Rich is never good......for anything.
Lean mixtures cause high exhaust temps (and make more power) which is what destroyed the exhaust manifolds, catalytic converters and valve guides.